VETA 55: Veterinary Gross Anatomy - Module 1 PDF

VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM...

VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Contents I. Introduction to Anatomy........................................................................................................... 2 II. Anatomical Terminology....................................................................................................... 6 III. Introduction to Different Body Systems............................................................................. 12 The Locomotor Apparatus.......................................................................................................... 12 Skeletal system/Osteology........................................................................................................ 12 Arthrology................................................................................................................................. 15 Synovial joints (Diarthroses)................................................................................................... 16 Myology..................................................................................................................................... 20 The Integument and Related Structures.................................................................................... 24 Skin............................................................................................................................................ 24 The Endocrine System................................................................................................................. 28 1  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM I. Introduction to Anatomy The doctrine of morphology as the scientific study of the form and structure of organisms was founded by Aristotle. He defined morphology as the search for a common construction plan for all structures, while adhering to a strict methodological process. Where similarities can be found, the relation between form and function requires further clarification. This scientific approach set Plato’s best student apart from the early Greek natural philosophers and to this day is the principal method employed in all areas of basic research. Objectives: a. Define the terms anatomy and physiology. b. Differentiate between microscopic and macroscopic anatomy. c. Differentiate the different points of view in macroscopic anatomy with emphasis on special areas of greater difficulty. d. Identify and outline the ancestry, breed categories and taxonomic classification of the dogs. Anatomy is the study of the form, arrangement, and structure of the tissues and organs that compose the body. Physiology is the study of function. Anatomy and physiology describe two complementary but different ways to look at the animal body. Structure and function are inseparable as the foundation of the science and art of medicine. One must know the parts before one can appreciate how they work. It is fundamental to the art and practice of veterinary medicine. The term anatomy stems from the Greek word, ‘anatemnein’ which means to dissect, “to cut apart”, and the dissection of the dead is the traditional method used in anatomy. Anatomists do employ a host of other techniques to supplement the knowledge of gross anatomy obtained by use of the scalpel. Macroscopic anatomy, also called gross anatomy, deals with body parts large enough to be seen with the unaided eye, such as organs, muscles, and bones. The use of light microscopy and electron microscopy to study the structures invisible to the eye is a subdiscipline of anatomy known as microscopic anatomy. The discipline is also extended by the study of the stages through which the organism evolves from conception through birth, youth, and maturity to old age; this study, known as developmental anatomy, is rather broader in scope than classic embryology, which confines its attention to the unborn. The central focus of the anatomy now is to understand the relationships between structure and function, which can be described as functional anatomy. Like the remaining disciplines, macroscopic anatomy can be presented from different points of view with emphasis on special areas of greater difficulty. In so doing, the basic facts remain of course unchanged. Systematic, descriptive Table 1: Main Body Systems anatomy describes the animal body System Main Component with all its parts as systems of structure Skeletal Bones and joints and organ-systems, strictly divided from Integumentary Skin, hair, nails, and hooves one another and therefore without Nervous Central nervous system and peripheral attention to their natural nerves interdependence. Expansive Cardiovascular Heart and blood vessels descriptions treat many particulars and Respiratory Lungs and air passageways allow some-times the view to the Digestive Gastrointestinal tube and accessory important to be missed; nevertheless, digestive organs they are a necessary prerequisite to the Muscular Skeletal, cardiac, and smooth muscle remaining, subsequent kinds of Sensory Organs of general and special sense observations to which the descriptive Endocrine Endocrine glands and hormones anatomy has led. Systematic anatomy Urinary Kidneys, ureters, urinary bladder, and can be subdivided further into general urethra and special anatomy. General anatomy Reproductive Male and female reproductive treats of facts that are generally valid for structures the entire system of structure or the 2  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM organ-system. Special anatomy provides special data for these structure- and organ-systems that hold for individual structures, as for one bone. The main systems of the body are listed in Table 1. Comparative anatomy emphasizes anatomical correlations, similarities and variations between the individual animal species and human beings. Comparisons of anatomy between the individual species are very often informative and helpful for homology and determining the function of anatomical structure. Already Goethe utilized principles of comparative anatomy to good advantage with the discovery of the incisive bone of human beings. This bone occurs regularly in our domestic animals and only occasionally in human beings. With his study of the human skull, he encountered a specimen with a developed incisive bone. It was by comparison with the animal skull that he was able to identify the bone and establish its homology. Topographical anatomy emphasizes the varying position-relationship of anatomical structures and underlines the areas of application for clinical medicine. The relationship of anatomical structures is analyzed step by step and in doing so the whole structural plan of the body is regarded. Applied anatomy is directed clinically and emphasizes the relationship of anatomical structures from which treatments or diseases of animals can be determined or explained. In that way not only interdisciplinary cooperation and interest for the veterinary profession are promoted but also the learning of anatomy is made easier. Classification and Natural History of the Dog. Domestic dogs are probably the most polymorphic mammals referred to as a single species, Canis familiaris, and some workers have suggested that no domestic animal be given species designation. The alternatives are the use of subspecific names or breed designations. Because all members of the family Canidae are interfertile and human interaction has affected their hybridization and distribution throughout the world, it appears simplest to adopt one term for all purebreds, mongrels, and feral dogs. The anatomy of dogs varies tremendously from breed to breed. Some basic physical characteristics are identical among all dogs, from the smallest to the largest; most but not all dogs have long muzzles, large canine teeth, and long tails. Like most predatory mammals, the dog has powerful muscles, a cardiovascular system that supports both sprinting and endurance, and teeth for catching, holding, and tearing. Dogs have disconnected shoulder bones (no collar bone) that allow a greater stride length for running and leaping. They walk on four toes, front and back, and have vestigial dewclaws (dog thumbs) on their forelimbs and hind limbs. Dogs exhibit a diverse array of fur coats; they range from Table 2. TAXONIMIC CLASSIFICATION different coat textures, colors, markings, and patterns. OF DOGS Order Carnivora. Intelligent, flesh eating Kingdom Animalia mammals with prominent canine teeth, molars Phylum Chordata adapted for crushing and cutting, and a relatively Class Mammalia short alimentary canal. Toes are provided with claws Order Carnivora and behavioral characteristics which identify them as Family Canidae predators with strong family ties, devoted to the care Genus Canis of their young. Living carnivores are divided into two Species C. lupus super families: Canoidea: group of dogs (arctoidea) Subspecies C.l. familiaris and C.l. dingo [Canidae – dogs; Ursidae – bears; Otariidae – sea lion and walrus; Mustelidae – weasels and Procyonidae – racoons] Feloidea: group of cats (auluroidea) [Felidae – cats; Viveridae – civets and Hyaenidae – hyaenas]. Family Canidae. Distinct groups of dog and foxlike animals distributed throughout the world. Two characteristics distinguish the dog from other canids and, indeed, from all other animal species. The first is its worldwide distribution in close association with humans. The second is the enormous amount of variability found within the subspecies. The family Canidae is divided into 3 genera: Canis (dogs, wolfs, coyote, jackal), Vulpes (foxes) and Dusicyon (fox-like animals and South American foxes). The domestic dog (Canis lupus familiaris and Canis lupus dingo) is a domesticated form of the grey wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in human history. The word "dog" may also mean the male of a canine species, as opposed to the word "bitch" for the female of the species. These 3  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM are a carnivorous species which can adapt to a wide-ranging diet such as meat, but it can also include vegetables and grains. A few common human foods and household ingestible are toxic to dogs, including chocolate (theobromine poisoning), onion and garlic (throsulphate, sulfoxide or disulfide poisoning), grapes and raisins, macadamia nuts, as well as various plants and other potentially ingested materials. Dogs were domesticated from gray wolves about 15,000 years ago. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. Through selective breeding by humans, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal. The typical lifespan of dogs varies widely among breeds, but for most the median longevity, the age at which half the dogs in a population have died and half are still alive, ranges from 10 to 13 years. Breeds of Dogs. The Chinese were probably the earliest breeders of purebred dogs, several of which are still popular. Often there are several names for the same breed, because the name may change when the dog is introduced into another country; thus, the Borzoi is also known as the Russian Wolfhound, the German Shepherd Dog as the Alsatian, the Vizsla as the Hungarian Pointer, the Scottish Deerhound as the Irish Wolfhound, the Great Dane as the German Mastiff, the Chow-Chow as the Canton Dog, and so on. Several breeds are well known in one country and almost unheard of in another, such as the Canaan Dog of Israel and the Swedish Vallhund. A breed is any group of animals derived from a common stock and bred for their distinctive features, which are codified as the standard for the breed by those willing to recognize the breed. The French Bulldog, for instance, was probably derived from the English Bulldog, which it resembles in most features. Breeds of dogs are classified according to their purposes and do not necessarily represent genetic closeness or ancestry by the American Kennel Club: The sporting dogs (26 breeds: American Water Spaniel, Brittany Spaniel, Chesapeake Bay Retriever, Clumber Spaniel, Cocker Spaniel, Curly-Coated Retriever, English Cocker Spaniel, English Springer Spaniel, Field Spaniel, English Setter, Flat-Coated Retriever, German Shorthaired Pointer, German Wirehaired Pointer, Gordon Setter, Golden Retriever, Irish Setter, Irish Water Spaniel, Labrador Retriever, Nova Scotia Duck Tolling Retriever, Pointer, Spinone Italiano, Sussex Spaniel, Vizsla, Weimaraner, Welsh Springer Spaniel, Wirehaired Pointing Griffon); The hounds (24 breeds: Afghan Hound, American Foxhound, Basenji, Basset Hound, Beagle, Black and Tan Coonhound, Bloodhound, Borzoi, Dachshund, English Foxhound, Greyhound, Harrier, Ibizan Hound, Irish Wolfhound, Norwegian Elkhound, Otterhound, Petit Basset Griffon Vendeen, Pharaoh Hound, Plott, Redbone Coonhound, Rhodesian Ridgeback, Saluki, Scottish Deerhound and Whippet); The working dogs (25 breeds: Akita, Alaskan Malamute, Anatolian Shepherd Dog, Bernese Mountain Dog, Black Russian Terrier, Boxer, Bullmastiff, Doberman Pinscher, German Pinscher, Giant Schnauzer, Great Dane, Great Pyrenees, Greater Swiss Mountain Dog, Komondor, Kuvasz, Mastiff, Neapolitan Mastiff, Newfoundland, Portuguese Water Dog, Rottweiler, Saint Bernard, Samoyed, Siberian Husky, Standard Schnauzer, Tibetan Mastiff); The terriers (27 breeds: Airedale Terrier, American Staffordshire Terrier, Australian Terrier, Bedlington Terrier, Border Terrier, Bull Terrier, Cairn Terrier, Dandie Dinmont Terrier, Smooth Fox Terrier, Wire Fox Terrier, Glen of Imaal Terrier, Irish Terrier, Kerry Blue Terrier, Lakeland Terrier, Manchester Terrier, Miniature Bull Terrier, Miniature Schnauzer, Norfolk Terrier, Norwich Terrier, Parson Russell Terrier, Scottish Terrier, Sealyham Terrier, Skye Terrier, Soft-Coated Wheaten Terrier, Staffordshire Bull Terrier, Welsh Terrier and West Highland White Terrier); The toy dogs (21 breeds: Affenpinscher, Brussels Griffon, Cavalier King Charles Spaniel, Chihuahua, Chinese Crested, English Toy Spaniel, Havanese, Italian Greyhound, Japanese Chin, Maltese, Manchester Terrier (Toy), Miniature Pinscher, Papillon, Pekingese, Pomeranian, Poodle (Toy), Pug, Shih Tzu, Silky Terrier, Toy Fox Terrier and Yorkshire Terrier); The non-sporting dogs (11 breeds: American Eskimo Dog, Bichon Frise, Boston Terrier, Bulldog, Chinese Shar-Pei, Chow-Chow, Dalmatian, Finnish Spitz, French Bulldog, Keeshond, Lhasa Apso, Löwchen, Poodle (Miniature and Standard), Schipperke, Shiba Inu, Tibetan Spaniel and Tibetan Terrier) and The Herding Dogs (20 breeds: Australian Cattle Dog, Australian Shepherd, Bearded Collie, Beauceron, Belgian Malinois, Belgian Sheepdog, Belgian Tervuren, Border Collie, Bouvier des Flandres, Briard, Canaan Dog, Cardigan Welsh Corgi, Collie, German Shepherd Dog, Old English Sheepdog, Pembroke Welsh Corgi, Polish Lowland Sheepdog, Puli, Shetland Sheepdog and Swedish Vallhund) 4  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Self-Assessment Quiz 1. Differentiate microscopic and macroscopic anatomy. 2. Differentiate regional anatomy, systemic anatomy, comparative and topographical anatomy. 3. Differentiate general and special anatomy. 4. Give the taxonomic classification of dogs from Kingdom to Subspecies. 5. Who were probably the earliest breeders of purebred dogs? 6. A ____________ is any group of animals derived from a common stock and bred for their distinctive features? References: Colville T. and Bassert J.M. 2016. Laboratory Manual for Clinical Anatomy and Physiology for Veterinary Technicians, 3rd Ed. Elsevier, Inc Colville T. and Bassert J.M. 2016. Clinical Anatomy and Physiology for Veterinary Technicians, 3 rd Ed. Elsevier, Inc Budras, K., McCarthy, P.H., Fricke W. and Richter, R. 2007. Anatomy of the Dog. 5th Edition. Schlütersche Verlagsgesellschaft mbH & Co. KG, Hans-Böckler-Allee 7, 30173 Hannover Evans, H.E., de Lahunta, A. 2017. Guide to the Dissection of the Dog. 8th Edition. Elsevier Inc König, H.E. and Liebich, H.G. 2020. Textbook and Colour Atlas: Veterinary Anatomy of Domestic Animals. 7th Edition. Georg Thieme Verlag KG, Rüdigerstr. 14 70469 Stuttgart Germany Singh, B. 2018. Dyce, Sack and Wensing's Textbook of Veterinary Anatomy. 5th Edition. Elsevier Inc. Answers to SAQ’s 1. Microscopic anatomy is a subdiscipline of anatomy that uses light microscopy and electron microscopy to study structures invisible to the eye while macroscopic anatomy deals with body parts large enough to be seen with the unaided eye, such as organs, muscles, and bones. 2. Systemic anatomy describes the animal body with all its parts as systems of structure and organ-systems, Comparative anatomy emphasizes anatomical correlations, similarities and variations between the individual animal species and human beings. Topographical anatomy emphasizes the varying position-relationship of anatomical structures and underlines the areas of application for clinical medicine. Applied anatomy is directed clinically and emphasizes the relationship of anatomical structures from which treatments or diseases of animals can be determined or explained. 3. General anatomy treats of facts that are generally valid for the entire system of structure or the organ-system. Special anatomy provides special data for these structure- and organ- systems that hold for individual structures, as for one bone. 4. Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Family: Canidae Genus: Canis Species: C. lupus Subspecies: C.l. familiaris and C.l. dingo 5. Chinese 6. Breed 5  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM II. Anatomical Terminology Anatomic terminology is used daily in veterinary hospitals to facilitate communication among members of the veterinary staff. It also allows accurate information to be recorded in patients’ medical records. For example, the location of a laceration or bone break, the correct position of an animal for a radiograph, or the site of a surgical incision can all be described using anatomic terminology. It is extremely important that anatomic terminology becomes part of your everyday vocabulary. An understanding of the following planes, positions, and directions relative to the animal body or its parts is necessary to follow the procedures for dissection. Objectives: a) Describe the four anatomic planes of reference. b) List and describe the anatomic terms of direction. c) List and describe common regional terms for the body. d) List the components of the dorsal body cavity. e) List the components of the ventral body cavity. Certain descriptive terms are employed to indicate precisely and unambiguously the position or direction of body parts. There are terms used to indicate precise position and direction of parts of the body; terms applied to the limbs; terms to indicate relative distances from the center of the limb; terms to indicate relative distances from the surface and terms which apply to the basic movement of the parts of the body. Terms used to indicate precise position and direction of parts of the body. Plane: A flat surface, real or imaginary, passing through the animal, or part of it. The planes of the body are formed by any two points that can be connected by a straight line. Types of Planes ✓ Median or longitudinal: (divides the body into similar halves) divides the head, body of the limb longitudinally into equal right and left halves (Fig. 1). ✓ Sagittal: passes through the head, body, or limb parallel to the median plane (Fig. 1). ✓ Transverse or segmental: cuts perpendicular to the median plane, or at right angles to its long axis or an organ or limb (Fig. 1). ✓ Frontal (or coronal): perpendicular to the median and transverse planes (Fig. 1). ✓ Dorsal Plane: runs at right angles to the median and transverse planes and divides the body or head into dorsal and ventral portions (Fig. 1). 6  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM  Surfaces: The outer or external aspects of an object or body. Types of Surfaces  Ventral: the surface directed towards the ground. Towards or relatively near to the underside of the head or body.  Dorsal: the opposite surface to the preceding (i.e. towards or relatively near to the top of the head, back of the neck, trunk or tail). On the limbs, it applies to the upper or front surfaces of the carpus (knee),, tarsus (hock), metapodium (homologous to the hand and foot), and digits.  Medial or internal: a surface or structure which is nearer than another to the median plane (i.e. towards or relatively near to the median plane).  Lateral or external: a surface which is further than another from the median plane (i.e. away from or relatively further from the median plane).  Cranial: is the head-end of the body. A surface towards or relatively near to the head. On the limbs, it only applies to structures above the carpus and tarsus. You may also encounter the term cephalic which means the same thing.  Caudal: is the tail-end of the body. A surface towards or relatively near the tail. On the limbs, again it applies to structures above the carpus and tarsus.  Rostral: applies to the head region only. A surface towards or relatively near to the nose.  Oral: applies to the mouth region only. A surface towards or relatively near to the mouth.  Aboral: applies to the surface opposite to or away from the mouth region. Terms applied to the limbs  Proximal refers to relative distances of different parts from the long axis of the body; viz., those parts of the limb or limb structures that are nearest to the body or main mass. Thus, we have the proximal extremity of limb bones being the upper extremity and the proximal part of bone structures being mostly the upper parts.  Distal refers to that part of a structure that is furthest away from the main mass of tissue. In the appendages, it applies to the lower end of say a limb bone or even the free end of the limb. With reference to the thoracic limb (pectoral limb) or forelimb  Dorsal refers to the cranial face of the distal part of the forelimb. In addition, it can refer to the dorsum of the manus (homologue of the hand).  Palmar (the older term is VOLAR) refers to the face opposite the dorsal face.  Radial (equivalent to medial) that side of the forearm in which the radius is located.  Ulnar (equivalent to lateral) that side of the forearm in which the ulna is located.  Brachium (or arm) specifically the region from the shoulder to the elbow. Also, a general term used to designate an arm-like process or structure.  Axilla is the space between the thoracic limb and the thoracic wall. With reference to the pelvic limb or hindlimb  Dorsal: the anterior face of the distal part of the pelvic limb. In addition, it can refer to the dorsum of the pes (foot).  Plantar: refers to the face opposite the dorsal face.  Tibial (equivalent to medial): that side of the leg on which the tibia is located (medial).  Fibular (equivalent to lateral): that side of the leg on which the fibula is located (lateral). Terms to indicate relative distances from the center of the limb.  Axis is the center line of the body or any of its parts. In CARNIVORA (DOGS AND CATS), the functional axis of the limb passes between the 3rd and 4th digits.  Axial and abaxial are terms meaning pertaining to or being relative to the axis. e.g., the AXIAL SURFACE of a digit faces the axis while the ABAXIAL SURFACE faces away from the axis. 7  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Terms to indicate relative distances from the surface of the body  Superficial relatively near to the surface of the body, or to the surface of a solid organ.  Deep relatively near to the centre of the body or the centre of a solid organ.  External or outer away from the centre of a hollow organ.  Internal or inner close to, or in the direction of the centre of a hollow organ Terms which apply to the basic movement of the parts of the body  Protraction taking the whole limb forward.  Retraction taking the whole limb backward.  Extension the movement of one bone upon another in such a way that the angle formed at their joint is increased. Thus, the limb reaches out or is extended; the digits are straightened. Referring to the back it means that it is straightened.  Flexion the movement of one bone in relation to another in such a way that the angle formed at their joint is reduced. Thus, the limb may be retracted or folded; the digits are bent. Referring to the back it is arched.  Pronation as applied to the manus (hand or paw), the act of turning the palm backward (posteriorly) or downward, performed by medial rotation of the forearm. This is the normal position of the manus in quadripeds.  Supination as applied to the manus (hand), the act of turning the palm forward (anteriorly) or upward, performed by lateral rotation of the forearm. Dogs have some limited ability to supinate the manus  Abduction the movement of a part away from the median plane. NOTE: In front (anterior), behind (posterior), above (superior) and below (inferior) are terms often used in human anatomy and refer to the human body in the normal upright attitude. To avoid misunderstanding, these terms are not applied to the quadruped animal body. Their use in veterinary anatomy is restricted to certain areas of the head, e.g., upper and lower eyelids, anterior and posterior surfaces of the eye. Topographical Terms Parts of the body and body regions subdivide the body, including the Surface of the body. Parts of the body are head and trunk with neck, rump and tail, as well as the limbs. The body regions divide the surface of the body and can be subdivided into subregions. Figure 3 shows the different topographical terms in the body of the dog. 8  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Activity: Laboratory Manual Activity 1: Anatomical Terminology: Directional Terms 9  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM References: Budras, K., McCarthy, P.H., Fricke W. and Richter, R. 2007. Anatomy of the Dog. 5th Edition. Schlütersche Verlagsgesellschaft mbH & Co. KG, Hans-Böckler-Allee 7, 30173 Hannover Colville T. and Bassert J.M. 2016. Clinical Anatomy and Physiology for Veterinary Technicians, 3 rd Ed. Elsevier, Inc Colville T. and Bassert J.M. 2016. Laboratory Manual for Clinical Anatomy and Physiology for Veterinary Technicians, 3rd Ed. Elsevier, Inc Evans, H.E., de Lahunta, A. 2017. Guide to the Dissection of the Dog. 8th Edition. Elsevier Inc König, H.E. and Liebich, H.G. 2020. Textbook and Colour Atlas: Veterinary Anatomy of Domestic Animals. 7th Edition. Georg Thieme Verlag KG, Rüdigerstr. 14 70469 Stuttgart Germany Mills, P. 2003. Comparative Animal Anatomy. The University of Queensland, 2003 Singh, B. 2018. Dyce, Sack and Wensing's Textbook of Veterinary Anatomy. 5th Edition. Elsevier Inc. Self-Assessment Quiz Our first patient was a cat that got a chunk taken out of the tip of his nose by a feisty parrot. That wound was on the most (1) ____________ part of the cat’s head. He was not happy when I inserted the rectal thermometer in his (2) ____________ end. I’m glad my assistant had a good hold of a scruff of skin over his shoulder blades in his (3) ____________ area. A good way to avoid forgetting to clip the dewclaws when doing a nail trim is always to start with the dewclaw. It is located on the inside or (4) ____________ side of the paw. Then work out to the outermost nail on the (5) ____________ side of the paw. I saw a cat give a cow a backrub today. The cow was lying on its ventral surface in (6) ____________ recumbency. The cat was on the cow’s back, or (7) _________________ surface. Periodically the cat would slowly walk toward the cow’s head in a (8) ____________ direction, stopping occasionally to knead the cow’s back. When the cat reached the cow’s neck, it would turn around and do the same thing toward the cow’s tail, or (9) ____________ end. The cow seemed happy. Dog and cat spay incisions are usually made on the midline of the belly. This is called a (10) ____________ midline incision and the animal must be positioned in (11) ____________ recumbency. In the United Kingdom, cat spay incisions are often made on the side of the abdomen. This is called a (12) _______________ incision, and the animal must be positioned in (13) ____________ recumbency. When radiographing limb bones, we should include the joints above, or (14) ____________, and below, or (15) ____________, to the target bone to be sure we get the whole bone on the film. For a radiograph of the tibia (shinbone) and its trusty sidekick the fibula, we would have to include the (16) ________ joint (17) ____________ to the tibia and fibula, and the (18) ____________ joint (19) ____________ to the bones. When an animal stands squarely on all four feet, the surfaces of its front feet that are on the ground are the (20) __________________ surfaces. The surfaces of its hind feet that are on the ground are the (21) ____________ surfaces. The top/front surfaces of all four feet are the (22) ____________ surfaces. To position a cat for a ventral midline surgical incision into the abdomen, the animal’s ventral surface must face upward. It must be in (23) ____________ recumbency. For a dorsal midline spinal surgery incision in a dog, the animal’s dorsal surface must face upward. It must be in (24) ____________ recumbency. For surgical repair of a superficial laceration on the left side of a ferret’s chest, the animal must be positioned on its right side with its left side facing upward. It is in (25) ____________ recumbency. A ventral midline surgical incision is made along part of the (26) ____________ plane of the animal’s body. A surgical incision made 2 inches to the left of the ventral midline would be along part of a (27) ____________ plane. If a horse waded into a pond until the water was about midchest high, the surface of the water would represent a (28) ____________ plane through the animal’s body. After cooling off in the pond, if the horse stood in the doorway of the barn so its front, or (29) ____________, end was inside the barn and its back, or (30) ____________, end was outside, the doorway would represent a (31) ____________ plane through the animal’s body. 10  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Key: 1. Rostral 12. Flank 23. Dorsal 2. Caudal 13. Lateral 24. Sternal 3. Withers 14. Proximal 25. Right lateral 4. Medial 15. Distal 26. Median 5. Lateral 16. Stifle 27. Sagittal 6. Sternal 17. Proximal 28. Dorsal 7. Dorsal 18. Hock 29. Cranial 8. Cranial 19. Distal 30. Caudal 9. Caudal 20. Palmar 31. Transverse 10. Ventral 21. Plantar 11. Dorsal 22. Dorsal 11  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM III. Introduction to Different Body Systems Cells and tissues similar in structure and function are joined together to form individual organs or organ systems. These act synergistically to fulfill functions that define the organism and ensure survival. Objectives a. Identify, describe, and distinguish the external features of dogs. b. To classify the types of bones of dogs c. To name and identify the different bones of Carnivores. d. To classify the different types of joints e. To enumerate examples of different types of joints f. To define related terms in myology g. To classify types of muscle fibers h. To name and identify the different muscles in dog. i. To identify the different structures of the Endocrine System j. To be familiarized with the normal anatomic structure and location of organs with endocrine function. The Locomotor Apparatus The locomotor apparatus is a complex organ system whose primary function is mechanical. The skeleton and the muscles are the major elements comprising this system, forming, and maintaining the individual body shape and providing for the locomotion of body parts or the whole organism. The skeleton is composed of individual elements: the bones, cartilage, ligaments, and the joints that together create the body’s framework, the skeletal system. The skeletal system constitutes the passive part of the locomotor system, whereas the musculature represents the active part. Both parts form a functional unit that is integrated into the body’s circulatory, lymphatic, and nervous systems. Locomotion involves movement of the: head, vertebral column (spine), and limbs. Skeletal structures are necessary for maintaining rigidity of the body and for providing attachment for skeletal muscles, which are only able to exert their moment of action by virtue of being attached to bones. The system performs many metabolic functions at a cellular level. Hormones regulate a constant process of growth, modification, and breakdown. The term “locomotor system” does not do justice to this many-facetted system; therefore, this system is more appropriately referred to as the system of motion, stability, and support. Skeletal system/Osteology Osteology is the study of bones (ossa) that combine to form the skeletons of diverse animal species. Bones are cellular structures in which the extracellular fluid environment of the cell is surrounded by a rigid, calcified frame. Bones are composed of bone tissue which is sheathed inside and outside by the endosteum and periosteum, respectively, and the bone marrow, as well as the blood vessels and nerves supplying these structures. These components classify bone as an organ. Functions of Skeletal System. Support – it acts as an internal scaffold upon which the body is built. Locomotion – it provides attachment for muscles, which operate a system of levers, i.e., the bones, to bring about movement. Protection – it protects the underlying soft parts of the body, e.g., the brain. Storage – it acts as a store for the essential minerals’ calcium and phosphate. Haemopoiesis – haematopoietic tissue forming the bone marrow manufactures the blood cells. The skeleton can be divided into cranial (head) and post-cranial parts. The latter can be divided into three parts:  Axial skeleton – runs from the skull to the tip of the tail and includes the skull, mandible, vertebrae and also the sternum.  Appendicular Skeleton – the pectoral and pelvic limbs and the shoulder and pelvic girdles which attach (append) them to the body. 12  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM  Splanchnic Skeleton – bones that develop within some soft organs. In the dog and cat, this is represented by the os penis within the tissue of the penis. Forms of bony tissues Bones differ greatly in form, size, and strength, not only between species but also within the same individual. These characteristics of bone are determined greatly through genetics, but also static dynamic influences and structural changes due to nutrition during the juvenile and adult phases play an important role. Broad muscles or cordlike tendons create mechanical influences at their insertion points on the bone, leading to the development of a process, depression, tuberosity/protuberance, unevenness, ridge, or an edge. Blood vessels, nerves, or organs (i.e., the brain, the eye, the cochlea of the inner ear) can also influence the surface structure of bone. Despite the great variety of bones, they can be grouped according to common structural characteristics. These are as follows: long bones, short bones, flat bones, pneumatic bones, and irregular bones (Figure 4). Long bones (Fig. 5) are characterized by a shaft or diaphysis, formed from a thick, outer layer of compact bone, and an inner medullary cavity. Long bones have two ends, the proximal epiphysis, and the distal epiphysis, which are covered by a thin layer of cortical substance. Both extremities contain spongy bone, which, as the name implies, resembles an ossified sponge with delicate pores. Long bones form the basis of the limbs, i.e., upper arm (humerus), shin bone (tibia), or the metacarpal bones. Short bones can have different forms: cylindrical, cubic, or round. Such bones contain an extensive latticework of spongiosa in which haemoreticular tissue is present. Carpal and tarsal bones are the most common short bones in the body Flat and wide bones consist of two layers of compact bone (tabulae) surrounding either spongy bone (diploe) or air (sinus). This group contains for example the scapula, the iliac bone, or the ribs. Some bones of the skull are flat bones surrounding cavities of air (ossa pneumatica). These bones have formed through the subsequent resorption of bone substance and are lined with mucosa. Examples are the maxilla or the ethmoid bone. Sesamoid bones (ossa sesamoidea) are found close to the joints (i.e., the foot joints) and either lie beneath or are embedded in (i.e., patella) a tendon. Irregular Bones – these have similar structures to short bones but a less uniform shape; they lie in the midline and are unpaired, e.g., are the wedge-shaped bones of the skull: the sphenoid, presphenoid and basisphenoid bones. Pneumatic bones - these contains air filled spaces known as sinuses which have the effect of reducing the weight of the bone, e.g., maxillary and frontal bones. 13  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Splanchnic bone – this is bone that develops in a soft organ and is unattached to the rest of the skeleton, e.g., the os penis. Bone Composition. Dried bone consists of roughly 1/3 organic matter and 2/3 inorganic salts (CaPO4 57%, CaCO3 4%, MgPO4 2%, NaCl and Na2CO3 3%). Most of the inorganic salt is a form of calcium phosphate called calcium hydroxyapatite. Bone derives its hardness from the deposition of mineral salts within the soft organic matrix. It has a compressive strength of 20,000 lbs/in2 and a tensile strength of 15,000 lbs/in2. In behaviour, bone is like reinforced concrete: the organic matter (collagen fibres, equivalent to steel girders) resist tension and the inorganic matter (mineral salts equivalent to concrete) resist compression. Mineralization of bones is a compromise between increasing strength and increasing stiffness (making them more brittle). The combination of lightness and compressional strength is achieved by internal sculpturing with trabeculae (from the Latin: little beams) orientated parallel to compressional cortices. Bone is ALIVE: it requires oxygen and nutrients, it can grow, change shape, erode, become infected and die. Blood supply to bone (Fig. 6) The blood supply to bone is of critical importance in maintaining the health of normal bone and in assisting the repair process after damage, fractures, etc. There are 3 sources of afferent blood to a typical long bone: Nutrient Artery (usually single). This passes to the medulla via the nutrient foramen where it branches to proximal and distal medullary arteries through the marrow. These further divides to provide the major blood supply to the diaphysis and may anastomose with epiphyseal and metaphyseal arteries at each end of the bone. Metaphyseal Arteries. Numbers of these enter the proximal and distal metaphyses at all sides. Their final branches anastomose with the medullary arteries. Normally this anastomosis is at a capillary level so the metaphyseal arteries make little contribution to the medullary blood supply but if the nutrient artery is blocked, they can enlarge to take over the medullary supply. Periosteal arterioles. Pass to the diaphyseal cortex only at areas of strong fascial attachment. They supply the outer third of the cortex where they anastomose with branches of the medullary artery. Their extent and significance is questioned, but they may be important in bone repair following fracture. Bone Development. The process by which bone is formed is called ossification and there are two types: intramembranous and endochondrial ossification. The cells responsible for laying down new bone are called osteoblast; the cells that destroy or remodel bone are called osteoclast. Bones develop either in fibrous tissue (membranous or dermal bones – flat bones; mainly cranial or facial) or in cartilage (cartilage bones – long bones). Some bones e.g., the ethmoid and temporal bones of the skull, have components of both. Intramembranous Ossification. This is the process by which the flat bones of the skull are formed. The osteoblast lay down bone between two layers of fibrous connective tissue. There is no cartilage template. The loose mesenchyme in the region of the future bone is invaded by osteoprogenitor cells, which develop into osteoblasts. These lay down calcium salts on a randomly arranged framework of collagenous fibres to form woven bone. Osteoclastic erosion of and osteoblastic remodelling coverts this weaker woven bone into lamellar bone. This takes the form either of a continuous latticework of trabeculae i.e., cancellous (spongy) bone, or compact bone with Haversian systems, according to the stresses each region of the bone is required to endure. Osteoblasts in the periosteum lay down trabeculae in dense parallel sheets to form circumferential lamellae of compact bone. Blood vessels carry stem cells which colonize the marrow forming haemopoietic tissue. Endochondrial Ossification. This type of ossification involves the replacement of a hyaline cartilage model within the embryo by bone. The process starts in the developing embryo but is not 14  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM completed fully until the animal has reached maturity and growth has ceased. The long bones of the limb develop by this method. Table 1. Bone markings. Projections, Depressions and Openings Where Muscles and Ligaments Attach Term Description Example Crest Narrow ridge of bone; usually prominent Iliac crest Epicondyle Raised area on or above a condyle Lateral epicondyle of the humerus Fossa Shallow depression, often serving as an articular Olecranon and radial fossae of surface the humerus Line Narrow ridge of bone; less prominent than a Gluteal line on wing of ilium crest Process Generally any bony prominence; sometimes Crest, spine, trochanter, used to name specific prominences tubercle, tuberosity, etc.; olecranon process Ramus Armlike bar of bone Ramus of the mandible Spine Sharp, slender, often pointed projection Spine of the scapula Tuberosity Large rounded projection Deltoid tuberosity of the humerus Trochanter Very large, blunt, irregular-shaped process; Trochanter of the femur found only on the femur Tubercle Small rounded projection or process Greater tubercle of the humerus Projections That Help Form Joints Term Description Example Condyle Rounded articular projection Occipital condyle of the skull Cotyloid A deep articular depression Acetabulum of the hip joint Facet Smooth, nearly flat articular surface Superior costal facet of the vertebrae Head Bony expansion carried on a narrow neck Head of the femur Trochlea A pulley shaped, articular structure Trochlea of the femur Depressions and Openings Allowing Blood Vessels and Nerves to Pass Term Description Example Fissure Narrow, slit-like opening Palatine fissure Foramen Round or oval opening through a bone Foramen magnum Fovea A shallow, nonarticular depression Fovea capitis on the head of the femur Incisure A notch-shaped depression at the edge of a bone Semilunar notch of the ulna Meatus Canal-like passageway External auditory meatus Sinus Cavity within a bone, filled with air and lined Nasal sinuses with mucous membrane Sulcus Furrow-like groove Brachial groove of the humerus Arthrology Joints are formed when two or more bones are united by fibrous, elastic, or cartilaginous tissue. The degree of mobility between two bones or cartilage structures depends entirely on the form of the gap between them. There are three main types of joints and they are named according to their characteristic structural features: Fibrous (synarthrosis) joints, Cartilaginous (Amphiarthrosis) joints and Synovial joints. Fibrous joints are immobile joints and may ossify with age. A fibrous joint is found where little movement is necessary. The bones are held together by fibrous connective tissue. The union is 15  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM short, direct, and often transitory since the bones may fuse and ossify later in life. No joint cavity is present. Three types of Fibrous Joints are recognized: Sutures (Fig. 7b) are largely confined to the flat bones of the skull. They can be further classified by the shape of the opposing bones (undulating seams of the skull e.g., serrate, squamous, flat and foliate). Endocranial sutures are simpler than those on the surface of the skull, and they do not quite correspond to the outside skull sutures. The time of closure of sutures (to form a synostosis) varies in different species. Further growth of the brain is allowed while the sutures are open. Thus, if they close too early, the development of the brain may be affected. The bregma is the point on the top of the skull where the sagittal and coronal sutures meet. In young animals, this is occupied by a space (anterior fontanelle), which allows continued growth of the skull. Gomphosis (Fig. 7c) is the joint formed between a teeth roots in the dental alveoli and its socket by dense connective tissue, in this case the periodontal membrane. It allows slight movement, but firm attachment. Syndesmosis (Fig. 7a) is a fibrous joint with much intervening connective tissue, e.g., attachment of hyoid to skull, tibiofibular articulation. Cartilaginous joints (Amphiarthroses). Immobile joints, united by cartilage, ossify with age. These allow only limited movement, e.g., compression or stretching. They may be formed from cartilage (synchondrosis), fibrocartilage, or a combination of both. There is no joint capsule. Two types are recognized (Fig. 8): Synchondrosis = hyaline cartilage union, e.g., physis. These are mainly transitory joints found in growing bone. In the adult, osseous fusion mostly occurs. However, the costochondral joints remain throughout life. Symphysis (Fibrocartilaginous Joints) = [G. grow together] fibrocartilage union, e.g., pelvic symphysis; mandibular symphysis; (also, intervertebral disk). These are found in symphyses (pelvic and mandibular) and are important joints between vertebral bodies and sternebrae. No joint capsule is involved, and yet there may be movement. Between the vertebrae lie discs - intervertebral discs (intervertebral fibrocartilages). The discs consist of a central nucleus pulposus. This acts as a water cushion and augments elasticity of the joint. It is surrounded by an annulus fibrosum which is normally fibrous and relatively pliable. Synovial joints (Diarthroses) Synovial joints (Fig. 9) allow the greatest degree of movement. Joints can be differentiated according to the number of bones involved in the joint, the degree of movement possible or the form of the joint surfaces. In spite of such variation, joints share common structural and functional features: an extensive joint capsule, a joint cavity containing synovial fluid, and hyaline joint cartilage which covers the ends of the two or more bones forming the joint. They are characterized by: a joint cavity containing synovial fluid; a joint capsule, and articular cartilage. 16  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM The joint capsule is comprised of two layers: the outer fibrous layer and the inner layer (synovial membrane). The thickness and development of the outer capsule layer varies greatly and is mainly determined by the mechanical load placed on the area in question. This layer may also contain capsule ligaments, which strengthen the capsule on the outside of the joint. The fibres of the stratum fibrosum continue into the bordering periosteum or perichondrium. Since the blood supply to this layer is limited, injuries require a long time to heal. However, an abundance of sensory nerve fibres innervate the stratum fibrosum, which explains the pain experienced after injury to the capsule itself or through stretching of the capsule due to swelling within the joint. The synovial membrane lines the joint cavity and is replete with cells, blood vessels and nerves. The synovial membrane appears ivory in color with a slight yellow tinge and forms both synovial villi and synovial folds. Even within the same joint, these structures can differ greatly in number, size, form and location. This membrane can be further divided into the inner synoviocytes layer comprised of cover cells, the synoviocytes, and a subsynovial layer of tissue. Two types of synoviocytes are present in the intima synovialis: type-A synoviocytes are responsible for phagocytosis,; whereas type-B synoviocytes produce and secrete proteins. Joints are filled with a pale yellow, viscuous fluid, the synovial fluid, whose primary purpose is to lubricate the joint, thus reducing friction between articular surfaces. Synovial fluid is excreted by the synovial membrane into the joint cavity but also fills the tendon sheaths and is found in synovial bursa. Synovial fluid is composed of hyaluronic acid, sugar, electrolytes and enzymes involved in the nutrient supply of cartilage. Hydrarthrosis occurs due to increased production of synovia. Free joint bodies, or “joint mice”, are free-swimming intraarticular pieces of cartilage or bone resulting from a chip-fracture or ossification of synovial villi. Depending on their location they can be very painful. The joint cartilage is firmly attached to a thin, subchondral bone layer adjacent to the epiphysis. It is not covered by perichondrium and the surface facing the joint is very smooth. Joint cartilage is thin in the centre of a concave surface but thick in the centre of a convex one. Some areas of the joint cartilage in hoofed animals display a reduction in cartilage, forming synovial grooves. Cartilage matrix fibre bundles are arranged according to the mechanical forces of compression and tension. The hyaline cartilage matrix absorbs shock, is flexible and possesses viscoelastic properties. Similar to other types of cartilage, joint cartilage lacks nerves and, with a few exceptions, is not vascularised. The articular cartilage can be divided into the: superficial zone, intermediate zone, radial zone, and calcified zone. The superficial zone is comprised of tightly woven collagen fibres near the surface of the joint cartilage. These fibres arch towards the surface, where they run parallel to one another. This fibre pattern increases the stability of the surface joint cartilage. The middle layer of the cartilage, the intermediate zone, is structurally homogenous. The radial zone is comprised of cartilage fibres that partly unite to form radially organised bundles. In the calcified zone, collagen fibres anchor the joint cartilage to the bone and are for the most part calcified. This structure guarantees a strong attachment of joint cartilage to bone. 17  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Beneath the joint cartilage is a subchondral bone plate that includes parts of the calcified joint cartilage as well as a layer of lamellar bone. This plate supports dynamic functions of the joint, acts as a cushion protecting the cartilage from axial forces and promotes the metabolic supply of the deeper layers of cartilage. The metabolism of joint cartilage is anaerobic. The cartilage is supplied with nutrients, for the most part, through diffusion. To a lesser degree, nutrients can also reach the cartilage from the joint synovia or through the blood vessels of the bone marrow. The high proteoglycan content lends a high capacity for binding water molecules, which facilitates the intrachondral transport of metabolites. Joints are strengthened by intracapsular, capsular or extracapsular joint ligaments. Some joints contain fibrocartilagenous structures (menisci in the knee joint, disc in the jaw joint) that serve to stabilize the joint or to compensate for incongruent joint surfaces. Fat tissue can also build intra- articular depots providing additional cushioning. Synovial joints can be classified according to different characteristics: Number of bones forming the joint: o simple joints, involving only two bones (e.g. shoulder joint), and o compound joints, involving more than two bones (e.g. the wrist joint). Type of movement allowed by the joint: o uniaxial joints with: ▪ hinge joint (ginglymus): the joint axis is perpendicular to the long axis of the bones (e.g. elbow or tibiotarsal joint), and ▪ pivot joint: the joint axis is parallel to the long axis of the bones (e.g. atlantoaxial joint between the 1st and 2nd cervical vertebrae); o biaxial joints with: ▪ saddle joint: e.g. between the interphalangeal joints, and ▪ ellipsoidal joint: e.g. atlanto-occipital joint between the occipital bone and the 1st cervical vertebra; o multiaxial joints with: ▪ spheroidal or ball-and-socket joint: e.g. shoulder joint or hip joint, and o tight joints (amphiarthroses): e.g. sacroiliac joint. Form of the articular surfaces: o spheroidal or ball-and-socket joint: e.g. shoulder joint or hip joint, o cotyloid join: a spheroidal joint where the glenoid cavity (socket) covers more than half of the joint sphere (ball), e.g. the aviary hip joint, o ellipsoidal joint, e.g. between the occipital bone and the 1st cervical vertebra, o saddle joint, e.g. the interphalangeal joints, and o condylar joint, e.g. the femorotibial joint. Joints are also classified according to their functional characteristics: o hinge joint: allows movement in one plane. allows flexion and extension with limited rotation. The movable surface is usually concave (e.g. elbow joint, stifle). o Cochlear/condylar joint: consist of a convex surface (condyles) that sits in a corresponding concave surface; allows movement in two planes; has similar movement to a hinge joint (e.g. knee joint, which is also complex; hock). o spring or snap joint: a suspension joint as well as a hinge and cochlear joint, where the collateral ligaments attach eccentrically to the axis of rotation and proximal to the joint axis (in the neutral position of the joint, the collateral ligaments are under the greatest amount of tension; during extension or flexion, the tension in the ligaments decreases, causing the joint to spring into a position other than the neutral position, e.g. the elbow joint), o sledge or gliding joint: e.g. femoropatellar joint, o spiral joint: the collateral ligaments attach eccentrically, distal to the axis of rotation (the ligaments are shortest in the neutral position; during extension or flexion, the tension in the ligaments increases, slowly braking the motion, e.g. the stifle joint), o plane joints: a gliding joint, e.g. the joints between the articular processes of the vertebrae, and 18  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM o incongruent joints: joints where the articular surfaces do not correspond, as seen in the femorotibial joint or in the temporomandibular joint; the joint surfaces are rendered congruent through fibrous discs, the menisci in the femorotibial joint and the articular disc in the temporomandibular joint. Stability of joints The correct apposition of articular surfaces is sometimes disrupted by abnormal movement or by a blow - dislocation or luxation of the joint. A number of features normally prevent this.  shape of articular surfaces.  action of ligaments  action of muscles (or tendons)  cohesive force of synovial fluid. Different types of movement in joints o Flexion and Extension ▪ This is movement between two bones which normally lie at an angle to each other. – If the angle is reduced - flexion. 19  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM – If the angle is increased - extension. – Typical examples are in a ball-and-socket joint such as the shoulder joint or a hinge joint such as the tibiotarsal joint. o Gliding: This occurs in the joints between carpals and tarsals. o Abduction: Occurs in both fore and hind limb. o Adduction: Default position for both fore and hind limbs. o Rotation: For instance, the shaft of a long bone may rotate about its long axis. o Circumduction: (This movement has been described as a potential movement of the hip joint, but it is usually pathological). Myology Two types of muscle tissue are distinguished according to morphology and function: smooth muscle tissue: responsible for the contractile functions of the internal organs, lines the excretory ducts of glands, forms the blood and lymphatic vessel walls, and striated muscle: can be further divided into the skeletal and the heart musculature. The skeletal musculature is the active part of the locomotor system. It is generally referred to as the musculature or muscles. Striated muscle is that tissue attached to the skeleton and which is under voluntary or conscious control. Skeletal muscles are highly vascularized and innervated by cerebrospinal (sensory and motor) and autonomic (sympathetic and parasympathetic) nerves, which together build a functional unit. Expansive sheets of connective tissue, the fascia or aponeuroses, as well as synovial structures, such as tendon sheaths and bursae, support and protect the muscles in all of their various functions. The muscles provide power to move the skeletal frame; the ends of the muscle always insert in bone or cartilage. They act as levers, resulting in movement of individual body parts or the entire organism. Muscles also carry part of the body weight, help form the walls of the thoracic and abdominal cavities and support the activity of the internal organs (e.g., respiratory muscles, diaphragm). Skeletal (striated) muscle is composed of elongate, multinucleated cells (muscle fibers). It has three different types: Type I – slow contracting, fatigue resistant, aerobic metabolism, Type 2A – fast contracting, fatigue resistant, aerobic metabolism, and Type 2B – fast contracting, fatigue susceptible, anaerobic metabolism. Note: Skeletal muscle will not contract in the absence of a functional nerve supply (denervation atrophy occurs). One neuron innervates a variable number of muscle fibers. The neuron plus the muscle fibers it innervates constitute a motor unit. To produce a stronger contraction, the nervous system activates more motor units. Muscles with many fast twitch fibers, which use energy at a higher rate, are found where rapid acceleration (i.e., propulsion) is required i.e., the locomotory muscles. Muscles with many slow twitch fibers are found where a force to slow down or prevent movement is needed. They are economical and use little energy and are common in postural muscles where they oppose the force of gravity. Some muscles have both propulsive and postural roles e.g., the semitendinosus m. uses areas dense in slow twitch fibres during standing or quiet walking and uses areas dense in fast twitch fibres during violent action. Endurance is the ability of muscle fibres to sustain contraction over long periods and is dependent on energy obtained from aerobic metabolism. A typical high endurance fibre is relatively small to allow for diffusion of oxygen and nutrients; has a rich blood supply; a high density of mitochondria; and a high density of cytochromes and myoglobin. Thus, high endurance fibres are sometimes called red fibres and provide the colouring of red meat. Postural muscles are aerobic, but some propulsive muscles also have high endurance qualities. Basic Structure of Muscle A classic muscle shape has a thick fleshy central part called the belly (Fig. 11). Here, the connective tissue muscle sheath is continuous with the dense fibrous connective tissue of the tendon that attaches the muscle to a bone. A muscle is attached to a bone at two points: its starting point is 20  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM called origin; this moves least during contraction. Insertion of a muscle is the attached end where there is most movement. Aponeurosis – the tendon is drawn out into flat sheet of connective tissue, e.g. muscles of the abdominal wall. Sphincter muscles – forms a circular ring and serve to control the entrance or exit to a structure, e.g., stomach and bladder. Macroscopically, muscle fibers appear staggered, attaching to the aponeuroses at varying angle widths or to the bone with tendons of various lengths. The tendon can divide and radiate into the muscle, so that the muscle becomes imbued with tendinous tissue. The spreading of the tendon tissue in the muscles results in a pattern (tendon sheath) similar to a feather or a leaf. Muscles are classified according to their structure and fiber orientation: unipennate muscles with two parallel tendon sheaths e.g., ulnar & radial heads of the deep digital flexor muscle, bipennate muscles with double tendon sheaths e.g., infraspinatus muscle, and multipennate muscles with multiple tendon sheaths e.g., humeral head of the deep digital flexor muscle (Fig. 12). Accessory Structure: The muscles are supported in their many functions through passive structures such as the: fasciae, bursae or tendon sheaths. Muscles are individually sheathed in fasciae. The fasciae are expansive, thin and mesh-like sheets consisting of mostly collagen but also elastic fibres. These fibres are orientated in the same direction as the tension and stress forces acting upon the muscle. The mesh-like architecture of the fibres allows the fasciae to functionally adapt to changing muscle thickness resulting from muscle contraction. Fascia often serve as origin or attachment sites for muscles. By sheathing a muscle, fasciae provide a frictionless surface, allowing freedom of movement between individual muscles situated next to each other. Fasciae are located throughout the entire body and can be divided into a thinner, superficial fascia and a stronger, deeper layer. The superficial fascia encloses the superficial 21  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM skin muscles in most regions of the body. Especially in the horse, the deeper layers can be reinforced through elastic fibres that lend them a yellow sheen (tunica flava of the ventral abdominal wall). Synovial bursae (Fig. 13A) are enclosed in a capsule of connective tissue. They vary in size, often containing more than one compartment, and are always filled with synovia. They can be compared to small gel cushions located beneath tendons, evenly distributing pressure originating from the tendon. The structure of the bursae walls is similar to that of joints. Like the joints, the wall is comprised of two layers: the inner stratum synoviale and the external stratum fibrosum. The synovial bursae are found everywhere in the body where muscles, tendons or ligaments glide over bone. Inconsistent or facultative bursae may develop subcutaneously at various sites subjected to constant mechanical pressure. Synovial bursae are classified according to their location: subtendinous bursae, submuscular bursae, subligamentous bursae and subcutaneous bursae. Synovial tendon sheaths (Fig. 13B) are similar to the bursae, except that they completely sheathe the tendons like a tube, protecting the underlying tissues from pressure exerted by the tendon and reducing friction during movement. Tendon sheaths often form when the synovial membrane of a joint forms a recess, which then surrounds the tendon. Locomotion Natural movements involve many muscles working simultaneously or one after the other. When two muscles act together, they are said to be synergistic. If they work against each other, they are antagonists. During movement, one part is the fixed point and the other the moving point. The fixed point is every part that remains immobile due to its attachment to the trunk. The punctum mobile must be smaller and lighter than the fixed point. The function of a muscle can be derived on the one hand from its origin, placement and insertion and on the other hand, from its point of rotation. Most all-natural movements, for example, breathing, walking, trotting, or gallopping, are a rhythmic cycle of contractions and relaxations of antagonistic muscle groups. Even during relaxation, every muscle is under a certain amount of minimal tension, the muscle tonus. This state is caused by a reflectory and constant excitatory stimulus originating from the muscle spindles. Anasthesia invokes a hypotonus, a reduction in muscle tonus. Many muscles serve to hold a certain body part in position and therefore display a constant minimal muscle tonus. These muscles are sometimes passively supported by tendon-like tissue embedded in the muscle belly. In order for movement to begin, both the muscle tonus of the antagonizing muscle(s) and the force of gravity must be overcome. Muscle contractions are categorized based on what happens to the length of the active muscle during movement. A continual increase in the intrinsic muscle tension without a change in muscle length is an isometric contraction. At a certain grade of tension, the muscle slowly begins to contract and shortens (isotonic contraction), resulting in movement. A muscle exerts force on a joint according to the laws of lever systems. Depending on the number of joints a muscle acts upon, it can be classified as a: uniarticular muscle or, biarticular muscle or polyarticular muscle. 22  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM From this classification scheme, it is obvious that some joints are always moved together when one muscle contracts (obligatorily linked joints). Other joints move together only under unique circumstances (facultatively linked joints). Muscles can also be classified according to their functional effect on a joint as: extensor (m. extensor), flexor (m. flexor), adductor (m. adductor), abductor (m. abductor), sphincter (m. sphincter), dilator (m. dilatator), levator (m. levator), depressor (m. depressor), and rotator (m. rotator) with: supinator (m. supinator) and pronator (m. pronator). Muscle names may be latinized (flexor digitorum profundus) or anglicized (deep digital flexor). Muscle are named (originally in the human) for their: shape (deltoideus), location (brachialis), attachments (sternohyoideus), structure (biceps), function (supinator) and combinations of these (pronator quadratus; superficial digital flexor; serratus ventralis; flexor carpi radialis; etc.) Classification of Skeletal Muscle Intrinsic muscles. Lies completely within one region of the body where they have their origin and insertion. They act on the bones in that part only, e.g. when a dog bends its elbow, it is using the intrinsic muscles of the forelimb. Extrinsic muscles. Run from one region of the body to another and alter the position of the whole part, e.g., a limb, in relation to the other. The muscle that attaches the foreleg of the dog to the trunk are extrinsic muscles; they move the whole foreleg in relation to the trunk. Muscles are named for six physical characteristic: Action, shape, location, direction of fibers, number of heads or divisions, attachment sites. Connective Tissue Structures Histologic types of connective tissue: Loose areolar connective tissue — low fiber density, contains spaces that can be filled with fat or fluid (edema) [found throughout body, under skin as superficial fascia and in many places as deep fascia] Dense irregularly arranged connective tissue — high density of collagen fibers, oriented in variable directions [found dermis; deep fascia in some locations; periosteum; fibrous joint capsule] Dense regularly arranged connective tissue — high density of parallel fibers, forming sheets, bands, or cords [found aponeuroses; ligaments; tendons] Connective tissue structures identifiable in gross anatomy: Dermis [G. skin] — the physically tough/strong component of skin (deep to epidermis) Tendon — attaches muscle to bone (called aponeurosis when sheet-like) Ligament — attaches bone to bone (usually thickenings of fibrous joint capsules) [Note: visceral ligaments located in body cavities are entirely different structures] Fascia [L. band] — collagenous fibrous tissue that hold the body together superficial fascia = subcutaneous tissue between skin & muscles/bone (body wall); regionally variable in amount (site for subcutaneous injection); contains: cutaneous muscle, mammary tissue, fat (also edema fluid) [e.g., cutaneous trunci m.; superficial muscles of facial expression] deep fascia = packing/binding tissue surrounding muscles, bones, & organs; serves to compartmentalize skeletal muscles; forms several named structures, viz.,; named regional fascia, e.g., thoraco-lumbar fascia, fascia lata, etc. (fascia is named where it is thick & distinct (i.e., dense c.t. vs. loose areolar c.t. Retinaculum [L. rope or cable] fascia that binds passing tendons to the surface of the carpus or tarsus (also, transverse humeral retinaculum) Raphe [G. seam] fascia that joins right and left counterparts of a particular muscle at the midline (e.g., ventral abdomen = linea alba) 23  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Epimysium [G. on + muscle] fascia covering the surface of a muscle, depending on the muscle, it may be thin (transparent) or dense (opaque & white); also, Perimysium = c.t. around muscle fascicles; and Endomysium = c.t. within muscle fascicles) The Integument and Related Structures Integument refers to the skin, along with its associated hair, glands, pads and claws. The skin covers the entire exposed surface of the body and is continuous with the mucous membranes lining openings onto the body surface, for example, the digestive, respiratory, and urogenital systems. It serves multiple functions essential into life. It serves as Protection as it covers the entire external surface of the body and blends with the mucous membranes at the body’s several natural openings, protects underlying structures against: Abrasive, thermal or chemical injury and physical trauma (pads and skin in the nose), Invasion of microorganisms and Protects against desiccation and overhydration. It provides sensory information, most of the skin’s surface is generously a supplied with numerous types of general sensory afferent nerve endings (temperature, pressure, touch , pain). It also produces secretions like, Sebum – produced by sebaceous glands; The mammary gland – modified sweat glands; Pheromones – produced by specialized sweat glands. Also facilitates in the synthesis (Vitamin D) that is activated within the kidney and liver and increases the uptake and metabolism of dietary calcium. It also serves as storage for fat as adipose tissue or subcutaneous fat and acts as a thermal insulator. Skin also acts as Thermoregulator to prevent excessive heat loss and also to dissipate excessive heat. The shunting of blood away from the skin’s surface can minimize heat loss. In dog, the role of skin in dissipation of excessive body heat is minimal; most dissipation of excessive body heat in dogs occurs in pronounced panting. Sweat glands are present but are quite few in number as compared with the number in other species. Communication. Production of pheromones which are natural scents used for intraspecific communication. Scents produced for communication includes the circumanal glands of the anal sacs. The integument also provides a means of visual communication, e.g. dog raises its hackles when threatened. Skin The skin forms the external surface of the body and consists of two layers: an epithelial layer designated epidermis and a connective tissue layer designated dermis or corium. The dermis rests upon an underlying layer of connective tissue, the subcutaneous layer or subcutis. The latter consists of a fatty part, the panniculus adiposus, and a supporting fibrous part that, together, constitute the superficial fascia. The epidermis (Figs. 15, 16) is made up of a stratified squamous epithelium that is cornified (keratinized) at its surface. Thickness and degree of keratinization depend on the mechanical stress to which this layer is subject. The epidermis is composed of a deep, still living, layer, (stratum germinativum = basal layer) which, by mitotic division, furnishes cell replacement, a spinous layer, a cornifying, dying layer (stratum granulosum) as well as cornified cell layers, stratum lucidum and stratum corneum. In addition to the epidermal cells, there are melanocytes, langerhans’ cells, and merkel’s tactile discs, especially in the stratum germinativum. The function of the epidermis consists of the replacement of cornified cells as a protection from radiation from the loss and entrance of water into the body, from the entrance of parasites and for protection against trauma. With traumatic injury to the skin, healing is furthered by covering the exposed dermis by epidermal cells as soon as possible. The dermis or corium (Fig. 15) consists of a thin, loosely arranged papillary layer, the papillae of which are seated in corresponding depressions of the epidermis, and a dense reticular layer. The papillary layer contains mainly loosely arranged collagenous fibrils. The reticular layer consists of a plexus of coarse nondistensible collagenic fibers with a predominant course direction. Elastic fibers are present in both layers and function to restore the typical texture of the tissue following lacerations or other distortion of the skin (with respect to the cells that are found here, especially fibrocytes, fibroblasts, mast cells, plasma cells, macrophages and pigment cells, see histology). 24  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM The subcutis (Fig. 15) consists mainly of loose connective and adipose tissue. It is penetrated by connective tissue cords that fix the skin to the underlying fascia or periosteum. The panniculus adiposus is the layer of fat tissue within the subcutis. Functionally, the subcutis with its subcutaneous fat tissue serves as a cushioning tissue, serves for the storage of calories and water as well as thermoregulation. Its loose connective tissue functions as a gliding layer. Where the subcutis is lacking (lips, cheeks, and eyelids) this gliding function is lacking and the striated musculature ends here directly in the dermis. The blood supply of the skin is provided by larger arteries and veins of the subcutis that, owing to the mobility of the skin, have a tortuous course. They send branches to the dermis that form here two networks. The arterial network of the dermis [Fig. 15(9)] is located at the boundary with the subcutis and the subpapillary network [Fig. 15(3)] lies between the papillary and reticular layers and gives off subepidermal capillary loops into the papillary body. The corresponding venous plexuses have a comparable location. A further subfascial vascular plexus joins the blood supply of the subcutis. The blood flow can be cut short by arteriovenous anastomoses [Fig. 15(4)], thus avoiding the capillary bed, and in this way the vascularization of the skin is regulated. The papillary layer is especially well supplied with blood. These vessels dilate in order to give off heat and constrict to conserve body temperature. In this way they function like the sweat glands in thermoregulation. The venous plexuses also function as a place to store blood. The lymphatic supply is by lymph capillary networks that begin subepidermally and invest the hair follicles and skin glands. The nerve supply is by sensory and sympathetic neurons (sympathetic nerve plexuses invest the blood vessels and function to regulate the blood pressure and in thermoregulation). The skin can be considered as the largest sensory organ of the body. Numerous nerve terminals and terminal end corpuscles (e.g., meissner’s tactile discs and vaterpacinian lamellar corpuscles) serve as receptors for sensory stimuli. With loss of their myelin sheaths, free nerve endings penetrate the epidermis at particular sites of the body and serve to mediate the sensation of pain. Superficial fascia is not part of the skin; it underlies the skin and serves to bind with skin to the muscles beneath. It also provides pathway for vessels and nerves to reach skin. It has two layers: Superficial layer of superficial fascia – fatty and looses and Deep layer of the superficial fascia – it is membranous and stronger. 25  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Muscles present in the skin has two types: Contained in the skin and Muscles that lies beneath the skin. Arrector pilli muscles: are contained within the skin and are associated directly with hair follicles. From the name itself These muscles erect the hairs against the cold and in behavioristic displays. Cutaneous muscles: anchored in the dermis and closely affixed to the superficial fascia. Contraction of these muscles causes movement of the skin, or of structures associated with skin. Prominent cutaneous muscles include the sphincter colli, platysma, and cutaneous trunci. The Hairs (Fig. 15) cover nearly the entire body surface, except the planum nasale, anus, vulvar lips and limb pads. Hairs are cornified filiform structures that are formed by the skin. The hair is subdivided into the shaft, which projects beyond the surface of the skin, the root, which is obliquely oriented within the dermis and has at its proximal end an expanded part, the hair bulb. Hair root and hair bulb are in a divided epithelial root sheath. The outer part of the sheath is continuous with the superficial epidermis. Its inner part cornifies above the mouth of the sebaceous gland and will be shed. The connective tissue root sheath is continuous with the surrounding connective tissue. The epidermal and dermal root sheaths together with the bulb of the hair constitute the hair follicle. The parts of the hair are medulla, the cortex and the superficial hair cuticle, which consists of thin scale-like cornified cells and, the same as the medulla, is used for forensic species identification and individual diagnostic procedures. The arrector pili muscle terminates below the mouth of the sebaceous gland, attaching obliquely to the dermal sheath of the root of the hair. Its contraction results in erection of the hair (in human beings, this brings about the phenomenon of ‘goose pimples’). Contraction of the arrector pili muscle compresses the sebaceous glands and, in erecting the hair, increases the air space between the hairs and the skin surface for thermo-isolation. The hair coat depends on the breed and is characterized by the individual and group-like arrangement of the hairs, the different portions of the individual hair types (lead hairs, guard hairs, wool hairs) as well as by the density, length and color of the hairs. There are basically three types of hairs: The ‘lead’ hair or ‘main’ hair is long, stiff, and slightly curved. It is independent of other hairs and in the dog occurs only rarely. Guard hairs are shorter than the lead hair, arched near the tip and thickened. Both lead and guard hair types form the hair coat. The third and shortest type of hair is the wool hair. It is very thin, pliable and in its course slightly or strongly undulated. Guard and wool hairs pass in a bundle or tuft together from a compound hair follicle, in which case one guard hair is surrounde by the six to twelve wool hairs that accompany it. The wool hairs predominate in the coat of the puppy. In most canine breeds they lie under the hair coat and only in a few breeds such as the Puli and Commodore, do they project above the hair coat and form a superficial ‘wool coat.’ Sinus or tactile hairs are remarkably long, special forms of hair in the vicinity of the opening of the mouth. To receive tactile stimuli, the root of the hair is ensheathed by a blood sinus that is contacted by numerous sensory nerve endings. Owing to the great lever action of this long hair even the finest tactile stimuli result in stimulation of this receptor. The length of the hairs varies considerably and is dependent on breed. In the ancestors of the dog, who lived in the wild, the longest hairs are found on the dorsum and the shorter ones on the belly and head. But this pattern is mostly lost with domestication. In wild Canidae, the thickness of the hairs increases toward the belly (thickness is about 0.1 mm). The color of the hair is effected by the melanin content of the cornified cells as well as the inter- and intracellular air bubbles, especially of the medullary cells. The direction of the hairs characterizes the coat. That part of the coat in which the hairs have a uniform direction is called the Flumina pilorum. In a vortex, the hairs are arranged divergently or convergently with respect to a central point. By the crossing of converging lines of hairs, hair ‘crosses’ are formed. Hair growth is not a continuous process. A hair in the active growth phase is in anagen; after a variable length of time the bulb undergoes a regressive change (catagen) towards a dormant or resting phase (telogen). Anagen (growth period): the active phase of hair production when cells of the hair bulb are mitotically active, and the hair grows in length. Catagen (period of involution): transitory period during which cellular proliferation slowly decreases and finally ceases; hair bulb becomes a solid mass of keratinized cells resembling a club (club hair) and the hair detaches from the underlying matrix and is easily removed (that is where the hairs embedded in the bristles of your hairbrush come from every morning). 26  VETA 55: VETERINARY GROSS ANATOMY FIRST SEMESTER 2024-2025 JOJO D. CAUILAN, DVM Telogen (resting phase): transitional stage of the cycle where hair bulb atrophies; chemicals released from the dermal papilla wakens the follicle from its dormancy and it begins to renew itself for activity; it then changes back to the active anagen stage again. The Cutaneous Glands comprise sebaceous and sweat glands as well as the mammary gland, which is a modified sweat gland. The sebaceous glands (Fig. 15) open into the hair follicles and are present at a few sites of the body independent of the presence of hairs as at the transition of the skin to the cutaneous mucous membrane (lips, anus). Sebaceous glands are lobular. The peripheral cells have a high rate of mitosis and the daughter cells are pushed centrally to the lumen of the gland. The enlarged and aging cells break down (holocrine secretion) and the sebum thus liberated reaches the lumen of the gland. It passes by way of a short excretory duct to the lumen of the hair follicle and thus to the skin. Sebum makes the skin soft and pliable and gives the hairs a natural sheen. The sweat or sudoriferous glands are classified as merocrine (eccrine) and apocrine glands (odor glands). The merocrine sweat glands are usually coiled, unbranched, tubular glands. They occur in the dog only on the pads of the limbs. In human beings, real merocrine (eccrine) sweat glands are present in large areas of the skin surface. Apocrine sweat glands or odor glands are present over wide areas of the skin surface, but they are comparatively underdeveloped. These tubular glands open usually into the hair follicle. Their thick secretion has an alkaline reaction and is responsible for the individual species odor. In man, the glands are well developed but limited to a few regions of the body: anus, vulva, axilla. Mammary glands. A greatly modified sweat glands, which secrete milk for nourishment of the young. A unique feature of the class Mammalia where the taxonomic class is actually named. In males, they remain rudimentary throughout their life; in females they are subjected to conspicuous changes during pregnancy and during and after lactation. They are typically arrange in two bilaterally symmetrical rows extending from the ventral thoracic to the inguinal region. Number of pairs varies in breeds; large breed has six glands on each side of the midline while small breeds has typically four glands on each side. They are identified acc