Comparative Veterinary Macroscopic Anatomy PDF

Comparative Veterinary Macroscopic Anatomy 1 I. INTRODUCTION Definition of the Discipline Comparative Anatomy is the description and comparison of the structure of animals, and forms the basis for their classific...

Comparative Veterinary Macroscopic Anatomy 1 I. INTRODUCTION Definition of the Discipline Comparative Anatomy is the description and comparison of the structure of animals, and forms the basis for their classification. In this broad field of anatomy, the following things must be considered:  The structure and architecture or morphological forms of animals are not uniform, and hence cannot be standardized.  In each major group of organisms there is a general plan of organization.  Variations in details of the general plan are characteristics of the species; moreover, a constitutional plan is possible by which one individual may be differentiated from another. One method of study of veterinary anatomy is the SYSTEMATIC APPROACH in which the body is regarded as consisting of systems of organs or apparatus which are similar in origin and structure and are associated in the performance of certain functions. The divisions of systematic anatomy are: 1. Osteology- the description of bones and cartilages whose principal functions are support and protection of soft structures. 2. Syndesmology/Arthrology- the description of joints whose functions are to make rigid segments of bones. 3. Myology- the description of muscles and accessory structures that function to put bones and joints into useful motion. 4. Splanchnology- the description of viscera (includes the digestive, respiratory, urogenital apparatus, peritoneum, and ductless glands). 5. Angiology- the description of the organs of circulation (heart, arteries, veins, lymphatics, and spleen). 6. Neurology- the description of the nervous system whose function is to control and coordinate all the organs and structures. 7. Sense organs- the description of the eyes and ears whose function is to relate the individual to the environment. 8. Common integuments- the description of the skin and associated structures whose function is for temperature regulation and protection of inner structures. Review of Directional Terms and Planes 1. Cranial-is a direction toward the head. The lungs are cranial to the intestines (closer to the head). 2. Caudal- is a direction toward the tail. The intestines are caudal to the lungs (closer to the tail). 3. Rostral and caudal- are terms for direction within the head to mean toward the nose (rostral) or toward the tail (caudal). The cerebrum is rostral to the cerebellum. 4. Median plane- is one that passes through the body craniocaudally (from head to tail). It divides the body into equal right and left halves. 5. Sagittal plane- is any plane parallel to the median plane, and except for the mid-sagittal plane (which is another name for the median plane), it would be either to the right or to the left of the median plane. 6. Transverse plane- is at right angles to the median plane and divides the body into cranial ad caudal parts. 7. Frontal plane- is at right angles to both the median and the transverse planes and would divide the body into dorsal (upper) and ventral (lower) segments. 8. Dorsal- pertains to the back or upper surface of the animal. Often used to indicate the position of one structure of the body relative to another, e.g. nearer the back surface of the body. The kidneys are dorsal to the intestines. 9. Ventral- pertains to the undersurface of an animal, and as with dorsal, is often used to indicate the position of one structure relative to another. The intestines are ventral to the kidneys. 10. Medial- relates to the middle or center; nearer to the median or midsagittal plane. The heart is medial to the lungs. 11. Lateral- is opposite to the meaning of medial, e.g. away from the median plane. The ribs are lateral to the lungs. KHAN L. JUNATAS, DVM | Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 2 12. Superficial- pertains to the surface or to a structure situated near the surface. The skin is superficial to the muscles. 13. Deep (Profundus) - refers to the structure situated at a deeper level in relation to a specific reference point. The femur is deep to the quadriceps muscles. 14. Proximal- when referring to part of a limb, artery, or nerve, means it is nearest the center of the body or the point of origin. 15. Distal- means relatively further from the center of the body. The hoof is distal to the knee. 16. Palmar- refers to the caudal surface of the forelimb distal to the corpus (joint connecting radius, ulna, and metacarpals). Dorsal refers to its opposite cranial side. 17. Plantar- refers to the caudal surface of the hindlimb distal to the tarsus (also known as the hock). Dorsal refers to its opposite (cranial) side. 18. Prone- refers to a position in which the dorsal aspect of the body or any extremity is uppermost. A radiograph from this position with the film on the ventral aspect is identified as a dorsal-ventral (DV) view. 19. Supine- refers to a position in which the ventral aspect of the body or palmar or plantar aspect of any extremity is uppermost. A radiograph from this position with the film on the dorsal aspect is identified as a ventral-dorsal (VD) view. Note: The study of the body regions or parts of domestic animals is also a part of Topographical Anatomy. Please search for illustrations showing the body parts of carnivores, horse, cattle, pig, sheep and goat. As you find the definitions or descriptions of these specific body parts, do not forget also to know their functions or importance under clinical or field conditions. Anatomical Variations The general plan of construction is based on morphological principles: 1. Zygomorphism 2. Metamerism 3. Tubulation 4. Stratification o Principle of Zygomorphism  Each animal can be divided into right and left halves or ANTIMERES (opposite or paired parts).  Paired or Homotypical organs  Two organs being one on each side of the body.  Can be superficial (eyes, ears, nipples) and deep (ovaries, testes, kidneys).  Can show slight differences in size, location, and relations.  Unpaired organs (Unilateral or single median structure)  Morphological asymmetry  Examples: liver (right side), spleen (left side), heart Caudal surface of the liver of the dog (A), (predominantly deviated to the left) pig (B), horse (C), and cattle (D). The  Functional asymmetry  Predominance of use of one side over the other, e.g. median planes are indicated. The liver is right-handed and left-handed individuals. asymmetrical, less so in the dog, more  Ovulation in bovine occurs more frequently in the right so in the pig and horse, and most in ovary; in chicken, in the left ovary and oviduct. cattle, in which the bulk of the organ is displaced to the right. o Principle of Metamerism  Employs the rule of serial (segmental) homology), that is, organs or structures are arranged according to linear longitudinal series.  Homology (Greek, homos—same; logos—relation) pertains to corresponding attributes or similarities in structures.  Serial homology- the craniocaudal succession of similar or homologous segments. KHAN L. JUNATAS, DVM | Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 3  All in all, METAMERISM is a system of structures in which similar segments succeed each other craniocaudally. It is best seen in embryos and becomes less evident in adults. o Principle of Tubulation  Determines the presence of a dorsal tube (neural tube) and a ventral tube (gut) in the body of vertebrates. o Principle of Stratification  Governs the arrangement of organs and their parts in layers (ectoderm, mesoderm and endoderm) which are formed in the early stages of development.  Examples: Skin (adult), bones covered by periosteum and endosteum, vessels, and other viscera.  Skin o Epidermis 1. Stratum corneum 2. Stratum lucidum A, Ventral view of the cranial part of a 15-day-old pig embryo 3. Stratum granulosum after fusion of the endocardial tube. B, Transverse section of a 4. Stratum spinosum seven- to eight-somite embryo taken at the level of 5. 1, First 5. Stratum basale aortic arch; 2, neural tube; 4, foregut. o Dermis o Subcutis  Bones covered by: Transverse section through the gut. o Periosteum 1. Substantia compacta 2. Substantia spongiosa 3. Cavum medullare (medullary cavity)  Vessels 1. Tunica externa 2. Tunica media 3. Tunica mucosa  Other viscera (e.g. intestine) 1. Tunica mucosa 2. Tunica submucosa 3. Tunica muscularis 4. Tunica serosa Important Terms in Comparative Anatomy o Homology- refers to identical structures having the same origin and location in different animals.  Example: thoracic limbs of a horse and wings of a bird.  Homologous organs do not necessarily have the same function. o Analogy- indicates only identity of function.  Examples: wings of birds and insects; lungs of birds and gills of fishes. o Normal- in medicine means healthy; in anatomy, it presents different connotations: 1. It may be the most frequent structure (>50%) from a statistical standpoint, e.g. philtrum of a bulldog (harelip-like). 2. It may be the structure best fitted to perform optimal activities under physiological requirements, e.g. compound stomach of ruminants (reticulum, rumen, omasum, and abomasum). KHAN L. JUNATAS, DVM | Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 4 3. It may be the ‘best’ structures as a result of natural selection from an idealistic standpoint, e.g. teats of animals (horse, 1 pair; cow, 2 pairs; dog, 5 pairs; sow, 8−10 pairs). **Normal** It refers to the most frequent structural form, may indicate a regular structure or sometimes may imply correctness because abnormal means deformity. Normalcy sets the point of departure for identifying variations, anomalies, and monsters. o VARIATIONS  Slight deviations of the normal morphologic pattern of an organ.  Variant- is the deviated organ.  Two kinds of variations (Guyenot, 1950) 1. Somatic/Somations- appear in the body or soma of the animal and are not hereditary. 2. Germinal or Mutations- occur in the germ cells and are hereditary.  The deviation can be: 1. An increase in the number of parts 2. Reduction of parts 3. Modification of form  Rudimentary- ‘imperfectly developed’; VESTIGIAL. A rudimentary organ may sometimes reach full development, and then become atrophied.  Atrophy- means a decrease in size of a normally developed organ or tissue.  Variations can be found in deviations of: 1. Holotopy- the relation between the organ and the body as a whole, e.g. heart- left side (right side, ectopic cordis). 2. Syntopy- the relation of the structure and its immediately adjacent organs, e.g. kidneys are bean- shaped or lobulated (fused ren arcuatus). 3. Idiotopy- the relation of the parts of an organ among themselves, e.g. number of digits/metatarsals. 4. Histotopy- the relation of the layers, coats or tissues of an organ among themselves, e.g. hyperkeratinization (increase in the number of cells in the epidermis). o ANOMALY  A severe deviation for the normal pattern accompanied by alteration or impairment of function.  Examples: harelip, cleft palate, cervical rib in man o MONSTER/MONSTROSITY  A severe anomaly, incompatible with life. Such malformations are dealt within teratology.  Teratology is the study of the causes and effects of congenital malformations and developmental abnormalities. General Factors of Variations: 1. Age 4. Biotype 2. Sex 5. Evolution 3. Race 6. Environment o Age  Differences in size (newborn, small or miniature; adult, large)  Microscopic and macroscopic variations in organs.  The thymus (due to age) grows until sexual maturity, and then becomes an atrophied organ in a relatively short period.  Some age-dependent variation of the individual: 1. Abrasion- modification of shape of the incisor crown in equine, bovine, and carnivore 2. Presence of large numbers of horn rings in old bovine 3. White hair on the head of aged equine 4. Thinning of the rostral border of the mandible of old equine 5. Loss of cutaneous elasticity mainly in old canine and bovine 6. Reduction of cloacal bursa in adult fowl (bursa of Fabricius B lymphocytes) 7. Reduction in size of paranasal sinus in adult dogs o Sex  Sexual dimorphism means physical or behavioral differences associated with sex; males and females of same species are different in appearance.  Differences are easily recognized in all species of domestic animals especially during the appearance of secondary sexual characters.  Examples: 1. Adult bony pelvis of a female is quite different from that of a male (larger and roomy). 2. Canine teeth in horses usually fail to erupt in mares and when present, they are vestigial. KHAN L. JUNATAS, DVM | Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 5 3. Dorsal pubic tubercle- well-developed in males mainly in bovine and underdeveloped in females and castrated males. 4. Plumage of fowl- longer and richer in color tones in males than in females (for attraction and seduction). 5. Height of females (mainly in turkeys and chickens) is less than that of males. 6. Crest and dewlap- smaller in females than in males. Dewlap is a loose skin under the throat and neck which maybe pendulous in some breeds of species. 7. Spur- is present in male chickens. Spur is a sharp, horn-covered, bony projection from the shank of male birds of some species. o Race  Regarded as “a population which differs significantly from other population with respect to the frequency of one or more of the genes it possesses.”  Defined phenotypically as a population whose members, though varying individually, are distinguished as a group by a certain combination of morphologic and physiologic characteristics which they share because of their common descent.  Examples of breed variations: 1. Dewlap present in Bos indicus and absent or rudimentary in Bos Taurus 2. Umbilical preputial fold present in Bos indicus and poorly developed in Bos Taurus 3. Hump present in Bos indicus and absent in Bos Taurus 4. Long, pendulous preputial fold in Bos indicus and the short, non-pendulous one in Bos Taurus 5. Absence of a horn button in 3 breeds of Bos Taurus (Polled Angus, Polled Hereford, Polled Shorthorn) 6. Direction of horns: vertical in Bos indicus; upward and lyre-like in Guzerat; downward, outward and backward in Gyr 7. Auricula (Auris externa) is little, movable, long, pendulous in Bos indicus, except in Nelore, which presents a short and movable one similar to Bos taurus. 8. Auricula, the bones of the face, the number of vertebrae, the color and arrangement of hair are different in three breeds of swine. 9. Dorsal outline, the form and profile of the skeleton of the head, the height and length, the weight in breeds of equine. 10. The head (Dolicocephalic- Collie and Russian Wolfhound; Mesocephalic/Mesaticephalic- Setter; Brachio/Brachycephalic- Boston Terrier and Pekingese) 11. Height (long limbs in Greyhound; short limbs in Bassethound and Daschund) 12. Dorsal line, the body outline, the auricular differ in breeds of canine. o Biotype  Constitutional anatomy is related to physical attributes of the body. This pertains especially to the proportion of its parts, as exemplified by the short, tall or stout or thin animal.  Biotype or Constitution refers to pertinent morphological, biochemical, physiologic, and pathologic (and even psychiatric) features and tendencies of the individual. o Evolution  Example is the orthogenesis in horses. o Environment  The development of economic characters (milk yield, meat conformation) depends on the environment (food supply, etc.) in which the animal is reared and kept. Variability and Selection o Selection and breeding together of animals which show variability in any structure seem to intensify the variation. Specific Variations: 1. Suburethral diverticulum of the cow (not found in mares, bitches, sows) 2. Preputial diverticulum of the pig (boar) 3. Urethral fossa of the horse 4. Absence of gallbladder in the horse 5. Presence of the guttural pouch in the horse (peculiar) 6. Absence of maxillary incisors in ruminants KHAN L. JUNATAS, DVM | Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 6 7. Presence of penis bone in dogs 8. Ossification of the cartilage of the interatrial septum (ossa cordis) in old bovine 9. Presence of muscular fibers in the proximal sesamoid ligament of the young bovine 10. Ossification of the sclera of adult aves 11. Nictitating membrane or third eyelid is fully developed in rabbits and aves; partially developed in horses; less developed in bovine; and rudimentary in dogs and man. KHAN L. JUNATAS, DVM | Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 7 I. OSTEOLOGY Osteology- (G. Osteon bone + logos study) is the study of bones. Bones or Osseous tissue- the hard, semi-rigid, calcified connective tissue forming the skeleton. Skeleton- refers to the framework of hard structures which supports and protects the soft tissues of animals. The skeleton may be divided primarily into three parts: 1. Axial skeleton- includes the skull, vertebral column, ribs and sternum 2. Appendicular skeleton- pelvic and pectoral limbs 3. Splanchnic/visceral bone- consists of certain bones developed in the substance of some of the viscera or soft organs, e.g., entoglossal bone and os sclera (birds), os penis (dogs), os cordis (ruminants), and the os rostra (pig). Classification of bones (according to shape): 1. Long bones- elongated cylindrical form (shaft; body, corpus; diaphysis) with enlarge extremities (epiphysis). They occur in limbs and act as supporting columns and as levers. 2. Short bones- similar dimensions in length, breadth and thickness. They diffuse concussion. Examples are the carpus and tarsus. 3. Flat bones- large area for muscular attachments and for protection of organs. Examples are the scapula and some bones of the skull, os coxae, and ribs. 4. Irregular bones- with varied functions; for support and ligamentous attachment. Examples are vertebrae, base of the skull (occipital, temporal) and certain facial bones. Some specialized varieties of bones: 1. Sesamoid bones- found within tendons to prevent injury and increase the leverage exerted by the muscle, e.g., patella (kneecap), fabellae, and navicular bone. 2. Splanchnic bones- as mentioned above, develop in soft organs, remote from the rest of the skeleton 3. Pneumatic bones- in the skull containing the paranasal sinuses, which communicate with the nasal cavities. A long bone (bovine humerus) sectioned longitudinally. 1, Articular cartilage; 2, spongy bone; 2′, epiphyseal cartilage; 3, compact bone; 4, periosteum, partly reflected; 5, nutrient foramen; 6, marrow cavity; 7, roughened area for attachment of muscle or ligament; 8, distal extent of medial epicondyle; 9, tendons of origin of carpal and digital flexors. depressions and projections. articular/nonarticular one by one, please review the bones of the domestic animals NOTE: Before you take up the Chemical and physical properties of bone:  The composition in 100 parts of ox bone of average quality: Gelatin------------------------------------------------ 33.30 Phosphate of lime--------------------------------- 57.35 Carbonate of lime---------------------------------- 3.85 Phosphate of magnesia--------------------------- 2.05 Carbonate and chloride of sodium------------- 3.45 100  Fresh dead bone has a yellowish white color; when macerated or boiled and bleached, it is white.  S.G. of fresh compact bone- 1.9, very hard and resistant to pressure. VERTEBRAL COLUMN/SPINE o Consists of a large number of separate bones called vertebrae and extends from the skull to the tip of the tail. 1. Fixed/false vertebrae- fused vertebrae. 2. Movable/true vertebrae- o Five regions: Cervical (C), Thoracic (T), Lumbar (L), Sacral (S), Caudal/Coccygeal (Cy/Cd) KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 8  Comparative: Vertebral Formula of Domestic Animals Cervical (C) Thoracic (T) Lumbar (L) Sacral (S) Caudal (Cy) Dog 7 13 7 3 20-23 Ox 7 13 6 5 18-20 Horse 7 18 6 5 15-21 Pig 7 14-15 6-7 4 20-23 Goat 7 13 7 5 16-18 Sheep 7 13 6-7 4 16-18 Chicken 14 7 14 6 Carabao 7 13 6 4 14-18  Parts of a typical vertebra: 1. BODY- broadly cylindrical, flattened; cranial (convex), caudal (concave). 2. ARCH- pedicles and laminae. **Body and arch- form a bony enclosure of the vertebral foramen. Putting all the vertebral foramina together, the vertebral canal is formed where the spinal cord and its coverings and vessels are located. 3. PROCESSES- Spine, transverse, articular, mamillary, accessory.  Articular- two cranial and two caudal.  Spine- single, projects dorsally from the middle of the arch.  Transverse- two in number and project laterally from the sides of the arch and body. In the cervical region, from the st th 1 to 6 , the transverse processes are pierced by the transverse foramen, which contains the vertebral artery, vein and nerve.  Mamillary- is found in most mammals on the caudal thoracic and cranial lumbar vertebrae.  Accessory- when present is found between the transverse and caudal articular processes. CERVICAL VERTEBRAE (Neck) o Massive and rectangular; longer than the vertebrae in other regions  Atlas and axis (ATYPICAL)  Remaining five (TYPICAL) o ATLAS st  1 cervical vertebra; the most unusual of all the vertebrae.  COMPARATIVE: Landmark Features in Domestic Animals Foramina Alar foramen is absent in carnivores; there is alar notch or incisures, instead. Transverse foramen is absent in ruminants. Lateral vertebral foramen divided into two in goats. The wings of the sheep atlas project posteriorly. In horse, three foramina are present—lateral vertebral, alar, & transverse foramina. In pig, the transverse foramen is situated in posterior border wing. o AXIS (Epistropheus)  Is the longest vertebra.  COMPARATIVE: Landmark Features in Domestic Animals Axis The axis is long in all species except in the pig. Spinous process Spinous process extends cranially and caudally in carnivore; only caudally in the pig; bifid in horses. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 9 Odontoid process (dens) In ox and sheep is characteristically spout-shaped; in dog, it is typically tooth-like. o REMAINING CERVICAL VERTEBRAE (C3-C7)  Becomes progressively shorter as the series is followed toward its junction with the thorax.  On the third and the sixth bones the transverse process is perforated by a transverse foramen through which the vertebral vessels and nerve pass. th  7 cervical vertebra- is characterized by a taller spinous process, NO transverse foramen, single transverse process & presence of facets on the caudal extremity for the first rib.  COMPARATIVE: Landmark Features in Domestic Animals th th Transverse process (6 The 6 cervical vertebra of horse has a trifid transverse process. cervical vertebra) In other animals, the transverse process has a well-developed ventral plate. th Transverse process (7 In pig, the transverse process is divided and the transverse foramen is cervical vertebra) present. o Additional literature:  In the horse, the neck may be arched, straight or hollowed in the natural standing posture. The arched form (‘swan- or peacock-neck’) is characteristic of some breeds. The concave form (ewe- neck) is not prized, and for most breeds it is the straight neck that is held in greatest esteem.  Many shorthair cats can be described as cobby—an adjective suggesting a short, thick neck and a thick, deep and fairly short trunk that is carried rather close to the ground. THORACIC VERTEBRAE (Back) o Long spinous process, shortened, flattened bodies; costal facets; short transverse process, closely fitting arches, and low articular process.  COMPARATIVE: Landmark Features in Domestic Animals th th Withers In horse, the highest point of the withers corresponds to the 4 and 5 thoracic vertebrae. **The characteristic prominence of the withers is due to the great length nd th of the spinous processes of the 2 to the 9 thoracic vertebrae. o Additional literature: th th  In saddle horses, exostoses sometimes develop on the summits of 14 -17 thoracic spinous processes, bringing these into painful contact with their neighbors (‘Kissing spines’). LUMBAR VERTEBRAE (Loin) o Greater length and more uniform shape of bodies, lack costal facet; long, flattened transverse process, interlocking articular process, and prominent mamillary process.  COMPARATIVE: Landmark Features in Domestic Animals Transverse process A characteristic of Equidae is that the transverse processes of lumbars 4, 5, 6 and sacrum articulate (synovial) with each other. The articulation th th between 5 , 6 and the wings of the sacrum is constant. o Additional literature:  In pigs, variation almost always affects the thoracolumbar region. An increase in number is more common, possibly the result of selective breeding for this character: the loins are the most valuable part of the carcass, apart from the hams.  Sites for epidural administration of anesthetics:  Dog- lumbosacral space  Cat- last 2 lumbar vertebrae st nd  Horse- lumbosacral space; 1 and 2 caudal vertebrae st st nd  Cattle- 1 lumbar (flank anesthesia); lumbosacral space; 1 and 2 caudal vertebrae (tail block) KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 10  Pig- lumbosacral space SACRAL VERTEBRAE (Croup) o Vertebrae fused together (sacrum).  COMPARATIVE: Landmark Features in Domestic Animals Dorsal surface In carnivores and horse, it is marked by a number of spinous processes; there is a preserved independence. In ruminants, spinous processes fused to form a continuous crest. Degree of fusion of sacral vertebrae is least complete in pig; reduced or absent spinous processes. CAUDAL/COCCYGEAL VERTEBRAE (Tail) o In the tail; varies greatly, even within a single species. o The more proximal vertebrae of some species provide protection to the main artery of the tail in the form of ventral (hemal) arches, separate small chevron (V-shaped) bones connected to the undersurfaces of the bodies, or paired ventral (hemal) process. RIBS o The ribs (costae) are elongated, curved bones forming the skeleton of the lateral thoracic walls. o Each rib consists of:  Bony (dorsal) part- the rib proper  Cartilaginous (ventral) part- the costal cartilage. o The two parts meet at the costochondral junction. o A rib is also described as having: a shaft, and two extremities- sternal and vertebral. o The vertebral extremity presents the head, neck and tubercle. The head and neck articulates with two successive thoracic vertebrae; the caudal one is that with the same numerical designation as the rib. o The cartilage articulates with the sternum either directly or indirectly:  Sternal (true ribs) - articulates directly with the sternum by means of cartilage; known also as immobile ribs.  Asternal (false ribs) - their cartilages are fused to form the costal arch (the cranial boundary of the flank); they are called respiratory ribs because they are mobile.  Floating- no connection with the sternum, no cartilage and when present it is usually the last rib. o The First Rib- strong, short and straight; cartilage stumpy, articulates with the sternum at a tight joint that fixes the rib (this allows it to act as a firm base toward which the other ribs may be drawn on inspiration; the shaft widens greatly at the sternal extremity. A common feature of the first rib is the SCALENE TUBERCLE.  COMPARATIVE: Landmark Features in Domestic Animals Ribs In dogs, ribs have cylindrical shaft; relatively narrow resulting in wide intercostal spaces In horse, the ribs have narrow shaft and are strongly curved in dorsal third. In ox and sheep, have wide, flat shaft with long neck. In pig, the ribs have narrow shaft and of distinct angle.  COMPARATIVE: Ratio of sternal to asternal ribs Dog 9:4 Pig 7:7 (8) Ruminants 8:5 Horse 8:10 RIB PAIRS STERNAL ASTERNAL STERNEBRAE Horse 18 8 10 7/8 Ox 13 8 5 7 Sheep 13 8 5 7 KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 11 Pig 14/15 7 7/8 6 Dog 13 9 4 8 Chicken 7 5 2 0 STERNUM o Median segmental bone with three parts:  Manubrium- cranial part, generally projects in front of the first ribs and may be palpated at the root of the neck.  Body- composed of several segments (sternebrae) joined by cartilages that is later replaced by bone.  Xiphoid cartilage- caudal part, projects between the lower parts of the costal arches. It supports the most cranial part of the abdominal floor and gives attachment to linea alba.  COMPARATIVE: Landmark Features in Domestic Animals Number of sternebrae Dog- 8; Pig- 6; Ruminants- 7; Horse- 6 Manubrium Rodlike in cats and dogs Laterally compressed in large animals Body Cylindrical in dog, wide and flat in ruminants; The sternum in the horse looks like a ship’s keel or canoe-like in appearance. Xiphoid process Absent in the horse Xiphoid cartilage Xiphoid cartilage is narrow and short in carnivores and pigs and broad (thin and wide) and leaf-like in ruminants and horses. The Appendicular Skeleton Body Part Skeleton Terms Skeleton Body Part Common to Both Limbs Shoulder region Scapula, coracoid, Cingulum Os coxae (hip Pelvis (shoulder) and clavicle (girdle) bone) Ilium, pubis, ischium Arm, upper arm Humerus Stylopodium Femur Thigh (femur) (brachium) Forearm Radius and ulna Zeugopodium Tibia and fibula Leg (crus) (antebrachium) [Manus] Autopodium [Pes] Carpus (wrist) Carpal bones Basipodium Tarsal bones Hock, ankle (tarsus) Metacarpus Metacarpal bones Metapodium Metatarsal bones Metatarsus Digit (finger) Proximal, middle, Acropodium Proximal, middle, & Digit, toe & distal phalanges distal phalanges BONES OF THE FORELIMB SCAPULA (Shoulder Blade) o The only remaining bone in the pectoral girdle of most domesticated animals. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 12  COMPARATIVE: Landmark Features in Domestic Animals Shape of the scapula Distinctly triangular in ox and sheep; less so in dog and cat. Scapular cartilage Well-developed in horse; a broad and thin structure in horse, ruminants, and pigs. Spine of the scapula Divides the lateral surface of the scapula into almost equal supraspinous and infraspinous fossae in dog and pig; in the ox and horse, the spine is placed more cranially so that the supraspinous fossa is smaller than the infraspinous fossa. In horse, the spine fades out distally. Tuber spinae scapulae/ Absent in the dog but well-developed in pig and horse; poorly developed Trapezius tubercle in cat and ox; prominent in pigs (overhanging the infraspinous fossa). Acromion (Hamate Absent in pigs and horses process) Suprahamate process Caudal additional projection in the acromion found only in cat. HUMERUS (Brachial bone/arm bone) o The largest bone of the thoracic limb. It is a long bone that lies obliquely against the ventral part of the thorax, more horizontally in the large species than in the small.  COMPARATIVE: Landmark Features in Domestic Animals Size of humerus Relatively shorter and more robust in horses and cattle than in the small ruminants and carnivores. Greater (lateral) tubercle Divided into cranial and caudal parts in the horse and cattle. Larger than the lesser tubercle in dogs; more or less equal in horses. Lesser (medial) tubercle Divided into cranial and caudal parts in the horse and cattle Intertubercular groove Single in the dog and pig; divided by a low sagittal ridge in the ruminants (Bicipital groove) and a well-developed ridge (intermediate tubercle) in the horse. **The groove contains the tendon of the biceps brachii. Intermediate tubercle A prominence molded in the intertubercular groove of horses. Supratrochlear foramen Present in the dog, absent in the pig, horse, ox, and horse. ** The foramen connects the olecranon and radial fossae together. Supracondylar foramen The opening in the medial epicondyle present only in the cat. **The foramen gives passage to the median nerve and brachial artery. Lateral tuberosity Massive and overhangs bicipital groove in ox and sheep; in pig, it almost converts the bicipital groove into a foramen. Humeral condyle In large animals, it engages with the radius and has the form of a trochlea; in the dog and cat, it is divided into the medial area (trochlea) for the ulna and a lateral area (capitulum) for the radius. Has three fossae in the cat. RADIUS (L. Spoke of a wheel) and ULNA (L. elbow) o The two bones providing the skeleton of the forearm. In the standing position they are arranged with the ulna caudal to the radius in the upper part of the forearm but lateral in the lower part. o The radius is a simple rodlike bone which serves as the main weight-bearing bone of the forearm. It is usually much stronger than the ulna in ungulates, but less dominant in carnivores, in particular the cat. o The ulna is a long, thin bone serving mainly for muscle attachment and formation of the elbow joint. Its shaft is greatly reduced and its proximal extremity is prolonged beyond the articular surface (olecranon). KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 13  COMPARATIVE: Landmark Features in Domestic Animals Fusion of the two bones The ulna is completely fused (by ossification) in ruminants and horse, the distal part of the limb is fixed in the position of pronation; connected by fibrous tissue in the pig; In horse, the fusion reaches its extreme, in which only the upper end of the ulna remains distinct. Distal two-thirds of the bone disappears and it is just represented in the distal end of the radius by the lateral styloid process; The two bones are separate in the carnivores; about 45° of supination is allowed in dog, and somewhat more to the cat. Antebrachial Long and narrow in the dog, pig and chicken, reduced to two short interosseous space spaces in ruminants, and just one space in the horse. Proximal extremity of the Tends to be more circular in carnivores, in which some supinatory radius capacity remains; transversely widened in the others. Neck of the radius Distinct only in carnivores. Distal extremity of the Concave in its cranial part and convex in its caudal part in ungulates; radius has a slightly concave ovoid form in carnivores for some additional movements. Size of ulna Ulna is larger than the radius in pig and chicken; extremely slender in sheep. Length Radius is longer than ulna in horse; ulna is longer than the radius in others. Olecranon In dogs has a trituberculate summit. CARPAL BONES o In domestic species the bones are clearly arranged into two transverse rows. o Proximal row: comprises (in mediolateral sequence) radial, intermediate, ulnar, and accessory bones; the last appears as an appendage projecting behind the carpus and is a prominent landmark in the live animal. o Distal row: the bones (in mediolateral sequence) is numbered one to five, although the fifth never appears as a separate bone but is either suppressed or fused with the fourth.  COMPARATIVE: Carpal Bone Dog Horse Ox Pig Sheep Goat Cat Radial        Intermediate      Ulnar        Accessory        1    2     FUSED FUSED FUSED 3     4        Total 7 7 6 8 6 6 7 o In the dog, the radial carpal bone is regarded by some workers as fused radial and intermediate carpal bone. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 14 METACARPAL BONES o There are five metacarpal bones for each digit; they are long bones designated numerically from the radial to the ulnar side. o The metacarpal skeleton of all species is somewhat compressed in the dorsopalmar direction.  COMPARATIVE: Domestic species Features of Metacarpal Bones Dog (5) 1, 2, 3, 4, 5 Horse (3) 2, 3, 4 **Mc III (Cannon bone/large metacarpal bone) **Mc II and Mc IV (Splint bones/small metacarpal bone) are reduced. Ox, Sheep (3) 2, 3, 4, 5 **Mc III and Mc IV (Cannon bone/Large metacarpal bone) are fused as chief metacarpal bone. **Mc V (Small metacarpal bone) is vestigial or rudimentary. Pig (4) 2, 3, 4, 5 **Mc III and Mc IV are the chief metacarpal bones, not fused. o What can be obtained from this table? 1. In dogs and cats, the first is retained as a nonfunctional dewclaw. The four functional digits are broadly equal, with the axis of the manus passing between the third and the fourth (PARAXONIC POSITION). 2. Pigs have entirely lost the first; the second and fifth are very much reduced, although each retains a complete skeleton. 3. In ruminants, the process has gone further; the metacarpal bones of the functional third and fourth are fused in a single bone that retains the evidence of its composite origin. 4. In the horse, only the third survives in functional form and its axis coincides with that of the limb (MESAXONIC POSITION). Remnants of the second and fourth Mc bones survive as splint bones that flank the third metacarpal or cannon bone. 5. Finally, as the number of metacarpal bones diminishes the relative stoutness of the surviving members of the series increases. The single (third) metacarpal bone of the horse therefore has a particularly strong shaft, whereas the individual Right manus of horse (B) and metacarpal bones of the dog are relatively much weaker. ruminant (C) DIGITS o Typically five in number and are designated numerically from the radial to the ulnar side, in correspondence with the metacarpus.  Comparative: Domestic species Features of Digits Dog (5) 1, 2, 3, 4, 5 Horse (1) 3 Ox, Sheep (4) 2, 3, 4, 5 Pig (4) 2, 3, 4, 5 o What can be obtained from this table? 1. Everything is almost the same with the metacarpal bones with some additions and minor differences. 2. Each digit has three digital bones, except in the first in the dog where there are only two digital bones. 3. The digital bones or phalanges (phalanx) are the proximal (first), middle (second), and distal (third). The first digit in the dog has only the proximal and distal phalanges.  Dewclaw (paradigit) - the first digit and the first metacarpal bone; not bearing weight. 4. The distal end of the digits is provided with a nail or claw (partly) in the dog and hoof (wholly) in the horse, ox, and pig. The latter three animals are also known as cloven-hoofed animals. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 15 5. In ruminants, although elements of four digits are present, those of the abaxial pair are vestigial. Digits 3 and 4 are the chief digits; digits 2 and 5 are called dewclaws (accessory digits). Each rd th accessory digit has two phalanges which do not articulate with the metacarpals. In ox, the 3 and 4 digits are fully developed weight-bearing digits consisting of three phalanges: proximal phalanx (long pastern as in the horse), middle phalanx (short pastern), and distal phalanx (coffin bone/pedal bone in horse). 6. In the digits of ox and horse, there are distinct, well- developed two proximal and one distal sesamoid bone. The distal sesamoid bone is also known as the navicular bone (L. little ship). Cursorial specialization involves raising the manus (and pes) from the primitive ‘flatfooted’ (PLANTIGRADE PLANTIGRADE) PLANTIGRADE posture demonstrated by bears. An intermediate stage, the DIGITIGRADE DIGITIGRADE posture, has been attained by dogs, which support themselves by digits only; it culminates in the UNGULIGRADE posture attained by ruminants, pigs, and horses in which only the tips of the digits, protected by hooves, give support. BONES OF THE HINDLIMB The Pelvic Girdle o Hip bones (Ossa coxarum) refer to the ilium, pubis and ischium. o The term bony pelvis refers to the ring of bone around the pelvic cavity composed of the two symmetrical hip bones, sacrum and first few caudal vertebrae. o Pelvic inlet- is the cranial opening into the pelvic cavity. o Pelvic outlet- is the caudal opening out of the pelvic cavity. ILIUM o The largest and the most cranial part of the os coxae. o It is divisible into two parts: 1. Cranial expansion (wing) - varies much among species; presents two surfaces, two spines and a crest. 2. Caudal shaft (body) - robust and columnar; the caudal extremity contributes to the formation of acetabulum. The ventral border of the shaft is marked by the low arcuate line that serves as part of the arbitrary boundary between the abdominal and pelvic cavities.  COMPARATIVE: Landmark Features in Domestic Animals Shape and orientation of Oblong with a more or less sagittal orientation in dog and cat; triangular the wings and almost vertical in horse and ruminants. Tuber sacrale Dorsally in smaller species, dorsomedially in larger species. Reduced to two low (cranial and caudal dorsal) iliac spines in carnivores but is prominent in large animals in which it is close to the spinous processes of the vertebrae. Close to each other at the midline in ox and horse so that very little space separates the two, widely separated in the dog (by a notch) and pig. Higher than the tuber coxae in the horse and about the same level in the dog and pig. Tuber coxae Ventrally in smaller species; ventrolaterally in larger species. Reduced to two low (cranial and caudal ventral iliac) spine in carnivores but is prominent in larger species (especially thick and massive in horse and ox). Forming the point of the hip at the dorsocaudal corner of the flank. It is also called as “hook” in the ox and is a palpable prominence on the lateral wing. Iliac crest/cranial border Thickened and convex in carnivores and pig; thin (sharp) and concave in horse and ruminants. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 16 Gluteal surface Faces dorsally in horse and ox, laterally in the pig and dog. Arcuate line Carries the psoas tubercle midway along its length except in the dog. It serves for the attachment of the psoas muscle. o Additional literature:  In dogs and cats  The convex iliac crest joining the ventral and dorsal spines provides a convenient site for bone marrow biopsy in larger breeds; it is too thin to serve this purpose in smaller animals.  In horses  Undue prominence of the sacral tubers (‘hunter’s bumps’) sometimes develops, especially in show jumpers and other horses subjected to similar repeated stress. PUBIS o The cranioventral part of the os coxae; it is essentially L-shaped, consists of cranial (acetabular) and caudal (symphysial) branches. o The lateral end of the cranial branch contributes to the acetabulum and is known as the body. o The cranial ramus extends from the body to the medial plane where it meets its fellow of the opposite side to form the pubis symphysis. o The caudal ramus passes caudally from the medial portion of the cranial ramus. ISCHIUM o Forms the most caudal part of the hip bone. o Consists of a horizontal plate extended cranially by symphysial and acetabular branches, one to each side of the obturator foramen. o Body- the extremity of the acetabular notch that contributes to the articular cup; a crest, the ischial spine, surmounts the body and the cranial part of this branch and which also extends onto the caudal part of the ilium.  COMPARATIVE: Landmark Features in Domestic Animals Ischial spine Marked by the origin of the gluteus profundus, it is relatively low in the dog and particularly high in ruminants. Ischiatic tuberosity A roughened swelling at the caudolateral corner of the plate, it is a horizontal thickening in the dog, and a conspicuously triangular swelling in cattle. It is the ‘pin bone’ in the ox. In most species it is subcutaneous, and it may be a visible landmark. Tuber ischiadicum is represented by a thickened ridge in the horse and dog, by a caudally directed process with a lateral tubercle in the pig, and by a trituberculate process in the ox. Are placed at a higher level than the acetabulum in the ox, at the same level in the horse, and at a lower level in the dog and pig. o Additional literature:  In horses  The slope of the pelvis may be estimated by visualizing the line joining the coxal and ischial projections. In the standard, generally approved conformation, this line forms an angle of about 30° with the horizon; from this it may be inferred that the sacrum is more or less horizontal.  When the angle is 30°, the animal is said to be goose-rumped. The croup is short and the hamstring muscles are reduced in length and in the leverage they may exert.  In ruminants  The slope of the pelvis may also be estimated. An angle larger than usual is associated with a more upright pelvic inlet; a smaller angle (flattened rump) requires the femur to be carried more vertically, which is a conformation thought to predispose to concussive trauma of the hip joint.  In pigs  The body and tuber of the ischium unite in very few pigs, and while the other tuber remains unfused, there is a risk of its becoming detached by the pull of powerful hamstring muscles that arise from it. Young sows are most commonly affected and are unable to rise when this happens; the condition is very painful, and there is no cure but slaughter. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 17 ACETABULUM o It is a deep articular cup (cotyloid) to which all three bones contribute; an additional small acetabular bone may be found in young animals. o The articular part is crescentic and is cut internally by a rough non-articular depression, the acetabular fossa. o The medial part of the rim is cut into by the acetabular notch. PELVIC GIRDLE/PELVIS:  COMPARATIVE: Landmark Features in Domestic Animals Pelvic cavity In dog- pelvic outlet is larger than the inlet. In pig, horse, and ox- pelvic inlet is larger than the outlet. Lateral wall of the pelvic cavity- formed by the broad ligament in the pig, ox, and horse, and by sacrotuberous ligament in dog. Sexual dimorphism Female has a concave pubic floor and large pelvic outlet. Male has convex pubic floor and small pelvic outlet. Dimensions of the girdle Are most important in species that carry a single large offspring; they are of little significance in polytocous species (those that normally carry a litter), in which the full-term fetuses are relatively small. o Additional literature:  In dogs and cats  The axis of the short pelvic canal is almost straight and the conformation appears well adapted for easy parturition.  Sexual dimorphism is not pronounced, and pelvic measurements have not been given much attention in small obstetrics.  The ischial tubers in cats stand closer together than in the dog, which gives the pelvis a more rectangular appearance in the VD view and a more confined pelvic outlet.  In horses  The pubic region presents a median swelling or ridge in young animals, and it retains this conformation in the stallion; however, the bone thins and the upper surface becomes markedly excavated in mares, especially those that have carried several foals.  The slope of the pelvic cavity places the pubic brim below the third or even fourth sacral vertebra in the mare but only the second in the stallion.  Viewed from the front, the inlet to the female pelvis is wide and rounded while that of the male is more angular and cramped, particularly ventrally.  The pelvic cavity of the mare has a truncated form, the longitudinal axis almost straight between the entrance and the exit; therefore, the pelvis of the mare is more favorably formed for ease of parturition than that of the cow—the entrance is wide, the exit less confined, the cavity generally more capacious, the axis without marked deflection, and a greater part of the lateral walls composed of soft tissue.  In cattle  The pelvic cavity of the cow becomes progressively narrower between the entrance and the exit. It also loses depth but in less regular fashion because a pronounced dip of the middle part of the floor results in a local increase in height before the caudal part slopes steeply upward to the shallow exit.  The pelvic outlet of the cow is roughly triangular; its width behind the iliac shaft is reduced by the inflection of the high ischial spine, and it becomes further reduced by the encroachment of the massive ischial tuber on the exit.  The lateral border is completed by the sacrotuberous ligament. However, its contribution is markedly reduced by the combined development of the ischial crest and crest and tuber.  Variations with age: KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 18  The pelvic inlet is almost uniformly wide in mature cows but considerably narrowed in its ventral part in heifers.  The cranial part of the floor raises a ridge over the symphysis in younger animals; in older cows, especially those that have carried several calves, the same region is level or sunken.  The male girdle, despite being significantly robust, encloses a cavity that is clearly less capacious; it is even more confined at the entrance, and beyond this the cranial part of the floor tends to be domed.  In sheep and goat  The long, slender iliac shafts approach the vertebral column at an acute angle that, in combination with the shortness of the sacrum, places the pecten below the second joint of the tail.  In pigs  From a lateral view, the pelvic floor and the iliac shaft meet at an angle that approaches 180°. This brings the pelvic inlet, which is large and oval, into a plane that faces almost directly ventrally into the abdomen.  The pelvic cavity slopes caudoventrally; the spines of the ischia are bent slightly inward to narrow the passage. FEMUR (Thigh Bone) o The largest bone in the skeleton; the strongest of the long bones.  COMPARATIVE: Landmark Features in Domestic Animals Fovea Round and central in the dog, wedge-shaped and extended to the medial periphery in the horse. Greater (major) trochanter It is as the same level as the head in the dog and pig, and higher than the head in the ox and horse. Divided into low cranial and high caudal parts in horses. Intertrochanteric line Absent in the pig and poorly developed in the horse, ox, dog and pig. Third trochanter It is salient only in the horse; absent in the ruminants. (trochanteric tertius) Supracondylar fossa At the caudodistal part of the shaft in horses; it is represented by the supracondylar tuberosity in the ox, dog, and pig. Trochlear tubercle The large prominence on the medial ridge of the patellar surface (trochlea) in the horse. The patella locks over this structure when the stay apparatus is in use. Shaft Distinctly quadrilateral in pig, cylindrical and curved in dogs. o Additional literature:  In dogs and cats  The greater trochanter is very nearly level with the femoral head; it provides a good guide to the position of the hip joint, which is not itself palpable.  Mid shaft fractures in carnivores: the shaft of the femur is so deeply embedded among the muscles of the thigh that only a general impression of its presence may be obtained in palpation. Despite this protection, the femur is the most commonly fractured bone, and most breaks occur about or below midshaft level. There is caudal displacement of the distal fragment due to the pull of the gastrocnemius muscle.  In horses  The two parts of the greater trochanter is separately identifiable on palpation. For the hip joint puncture, the needle is introduced between the two parts and is directed horizontally and craniomedially, at an angle of about 40° to the transverse plane.  The third trochanter and the later epicondyle are easily distinguished and may be used to reveal the orientation of the femur.  The femoral trochlea is markedly asymmetrical. The medial ridge is larger than the lateral one and is prolonged proximally to a terminal protuberance that is easily identifiable on palpation.  The trochlear surface comprises two distinct areas:  Gliding surface- the larger one, corresponds to the whole trochlea of most species and faces in a predominantly cranial direction.  Resting surface- the smaller one forms a narrow shelf above the gliding surface, from which it is sharply angled to face proximally. Only in extreme extension (e.g., during support phase of a walking stride or when the animal is standing squarely), do the resting surface engages with KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 19 the patella. However, this position is unstable and the patella is easily dislodged; it then slips back onto the gliding surface of the trochlea. PATELLA (L. Little plate, kneecap) o Largest sesamoid bone developed within the tendon of insertion of quadriceps femoris, the main extensor of the stifle. o It articulates with the patellar surface of the femur.  COMPARATIVE: Landmark Features in Domestic Animals Shape of patella Ovoid in the dog but prismatic or is broadly diamond-shaped in the horse and in cattle. The articular surface is divided in the horse. The more extensive backward-facing area engages with the trochlea during the greater part of the normal range of movement; the narrow strip at the apex makes contact with the femur only at the limit of extension. Patellar fibrocartilage In the horse and ox, there is a medial cartilaginous attachment of the patellar ligament with the patella. o Other sesamoid bones in the area: 1. Fabellae (L. bean) - two small sesamoid bones embedded in the heads (origin) of the medial and lateral parts of the gastrocnemius of carnivores. 2. Sesamoid bone of the popliteal tendon- also only in carnivores. This should not be mistaken for a chip fracture in radiographs. TIBIA AND FIBULA (Leg skeleton, L. crus) o Unlike the analogous elements of the forelimb, run side by side without any tendency to cross. o Tibia (‘shin bone’) - is medially located long bone; always larger of the two. It is large and prismatic which supports the weight and articulates distally with the talus (tibial tarsal bone). o Fibula (L. pin or skewer, ‘calf bone’)- is a long, much more slender, thin bone bearing little weight and is situated along the lateral border of the tibia, from which it is separated by the interosseous space of the leg. It is excluded from articulation with the femur and has only restricted contact with the hock skeleton.  COMPARATIVE: Landmark Features in Domestic Animals Shaft Dog and pig have complete shaft and two extremities (not fused); the fibula is reduced in stoutness but not in length, it is as long as the tibia. The shaft of fibula in ruminants is vestigial; the proximal extremity persists as a tear-shaped process fused to the lateral condyle of the tibia. In the horse, only the proximal half of the fibula remains, and the head is closely applied to the tibia. Interosseous space Runs the whole length of the leg in the pig but is limited to proximal half in the dog. Malleolar bone In ruminants, the lateral surface of the distal extremity of the fibula is isolated as a small compact malleolar bone that forms an interlocking joint with the tibia, completing the articular surface for the talus. Tibial crest Long and distinct in pig, short, prominent and marked with impressions in dog. Lateral malleolus Fused as a lateral swelling with the tibia of the horse while it articulates separately as the assimilated distal part in ox, sheep and dog. o Additional literature:  In dogs  Both the distal femoral and proximal tibial epiphyses generally fuse with their respective shafts th th th between the 6 and 12 months. The center for the tibial tuberosity fuses between the 8 and 10 months; while it persists, the cartilage line between it and the shaft is rather wide and irregular, presenting an appearance that stimulates avulsion of the tuberosity (Dyce, Sack & Wensing, 2010). KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 20  Growth plates in dogs unite by one year of age. The one for the tibial tuberosity can be mistaken for a fracture in all species (Pasquini, 1996).  The onset and completion of these fusions are somewhat delayed in cats.  In lean dogs the fibula may be palpated along its length, but in fatter and particularly well-muscled animals only the head and the distal half of the shaft may be felt with certainty.  In horses  The cochlea is flanked by medial and lateral malleoli.  In ruminants  The malleolar bone also takes part in the formation of the hock joint. TARSAL BONES (G. tarsos, flat; ‘hock’) o Arranged in three tiers between the crus and metatarsal region. o The proximal tier consists of two relatively large bones: the talus (tibial) medially and the calcaneus (fibular) laterally.  Talus (Ankle bone, tibial tarsal) - the largest bone of the tarsus, located on the dorsomedial side. It articulates by its trochlea with the tibia (the tibia and fibula in the dog).  Calcaneus (Heel, fibular tarsal) - situated at the fibular (lateral side), has a process, the sustentaculum tali, which supports the deep digital flexor tendon. The larger part of the bone, calcaneal tuber, projects proximally and plantarly behind the tibia as a free lever arm to which the common calcaneal tendon attaches. It ends in a thickening that is the basis for the ‘point of the hock’. o The middle tier comprises only a single central tarsal bone. st nd rd th o The distal tier comprises up to four bones, which are numbered (1 , 2 , 3 , 4 ) in mediolateral sequence; the lateral fourth tarsal bone is constantly present and, being much deeper than the others, intrudes into the middle tier.  COMPARATIVE: Bone Dog Horse Ox Pig Sheep Goat Cat Talus        Calcaneus        Central tarsal*   FUSED  FUSED FUSED  WITH 4TH WITH 4TH WITH 4TH 1  FUSED      2    FUSED FUSED FUSED 3     4*   FUSED  FUSED FUSED  WITH WITH WITH CENTRAL CENTRAL CENTRAL Total 7 6 5 7 5 5 7  Centroquartal bone (fused central and fourth tarsal bones) in ruminants.  Ruminants and pig have two trochlea to their talus. o Additional literature:  In horses  The distal surface of the talus which articulates with the central bone is flattened in the horse and more rounded in other species.  The proximal surface of the central tarsal bone is concave in most animals but flat in the horse.  Most common hock problems:  Spavin (arthritic changes) commonly affect the bones of the hock. Bone spavin or osteoarthritis of distal tarsal joint is the number one lameness in Standardbreds, common in KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 21 western horses, and jumpers. The ‘seat of the spavin’ is on the medial aspect, near the meeting of the third and central tarsal and third metatarsal bones.  Osteochondrosis dissecans is the second most common hock problem. The most common sites in tarsus are the intermediate ridge of the distal tibia followed by the trochlear ridge.  In ruminants:  In marked contrast to the horse, the talus carries a trochlea at each end.  The proximal trochlea articulates with the tibial cochlea and malleolar bone, forming the tarsocrural joint.  The distal trochlea articulates with the calcaneus behind and the centroquartal bone distally, forming the proximal intertarsal joint.  The conformation of the hindlimb, particularly the hock, is important in the selection of animals for breeding—the point of the hock should be vertically below the ischial tubers in both lateral and caudal views.  If they are too close the animal is said to be ‘cow-hocked,’ and its feet assume a wide stance. The opposite bow-legged conformation brings the feet closer together.  The normal angle of the hock joint (viewed from the side) is about 140°, which gives the metatarsus a slightly forward inclination.  When the angle is noticeably smaller, the hock sinks and the animal is said to be ‘sickle- hocked’; when it exceeds the normal, the animal is said to be ‘straight-hocked,’ a defect that may lead to ‘weak pasterns’ because of the reduced angle at the fetlock joint. METATARSAL BONES and DIGITS o The remaining bones of the hindlimb closely resemble those of the forelimb. o The metatarsal bones are longer (by about 20%) than the metacarpals and are more rounded in cross section.  COMPARATIVE: Domestic species Features of Metatarsal Bones Dog (4) 2, 3, 4, 5 st 1 may be present but only rudimentary, not connected with each bone, also known as dewclaw) Horse (3) 2, 3, 4 Mt III is also known as cannon bone or large metatarsal bone; Mt II and Mt Iv are also known as splint bones or small metatarsal bones. th o In ruminants, the 5 metatarsal bone is absent. A metatarsal sesamoid bone is present and is often called the ‘small metatarsal’ or metatarsal II.  Comparative: Domestic species Features of Digits Dog (4) 2, 3, 4, 5 Each digit has 3 digital bones Horse (1) 3 Has 3 digital bones Ox (4) 2, 3, 4, 5 Digits 3 and 4 has three digital bones each Pig (4) 2, 3, 4, 5 Each digit has three digital bones o First digit of dog, if present, consists only of two digital bones or only a terminal bone. o Just like in the thoracic limb, each principal digit in horse and ox has two proximal and one distal sesamoid bones. The Skeleton of the Head o The complete skeleton of the head comprises the skull, the mandible (lower jaw bone), the hyoid apparatus, the ossicles of the middle ear, and the cartilages of the ear, nose, and larynx. THE SKULL o It is a mosaic of many bones, mostly paired but some median and unpaired, that fit closely together to form a single rigid construction. o Two groups of bones of the skull: 1. Cranial- the caudal part that forms the cranial cavity where the brain is lodged. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 22  Occipital, interparietal, basisphenoid, presphenoid, pterygoid, temporal, parietal (L. Parles wall), frontal (L. Forehead), ethmoid and vomer 2. Facial- bony framework in the rostral part that supports the face.  Nasal, ventral nasal conchae, maxilla, lacrimal, incisive, rostral (pig), palatine, zygomatic, mandible and hyoid bones o Paired bones of the skull: 1. Cranial bones- interparietal, parietal, frontal, temporal, pterygoid **the parietal forms the greater part of the roof of the cranium. 2. Facial bones- maxilla (principal bones of the upper jaw), nasal, incisive (pre-maxilla), ventral nasal conchae, lacrimal, palatine and zygomatic o Unpaired bones of the skull: 1. Cranial bones- occipital, basisphenoid, presphenoid, ethmoid and vomer (Plowshare). In chicken, the occipital bone is paired. 2. Facial bones- mandible (L. Mandere to masticate) and hyoid o CRANIAL CAVITY- encloses the brain, with its membranes and vessels.  Dorsal wall- occipital, interparietal, parietal, and frontal bones  Lateral wall- temporal, frontal and presphenoid bones  Ventral wall- forms three fossae  Rostral cranial fossa- formed chiefly by the presphenoid; it supports frontal and olfactory parts of the cerebrum.  Middle nasal fossa- formed by the basisphenoid; it contains hypophysis.  Caudal cranial fossa- formed by the basilar of the occipital bone; it contains the medulla oblongata, pons and cerebrum. o FACIAL PART OF THE SKULL  Among the species, this part can show variations in length (horse vs. cat).  The dog shows great variation within the species whereas; it is fairly uniform in the other domestic species.  In dog, there are three types of skulls relative to the proportions of the facial bones and the cranial vault. 2. Mesaticephalic- average conformation; length of the skull is more harmoniously proportional to its width. 3. Dolichocephalic- has longer facial component; head is long and narrow, dorsal surfaces of nose and cranium form parallel planes that are divided at the level of the eyes by a break; underbite jaw (brachygnathism), external sagittal crest well developed, and zygomatic arches project less than the other. 4. Brachiocephalic- has a shorter facial component; the facial part is short and the cranium wide and globular, stop is pronounced, dorsal surface of the cranium is convex, much reduced external sagittal crest, eyes are widely spaced; most often prognathic.  MAJOR COMPARATIVE: Landmark Features in Domestic Animals Interparietal bone The bone found only in the horse and cat, between the two parietal bones, rostral to the occipital bone. In other species, it is present in the fetus but then fuses with surrounding bones before birth. Frontal bone Forms the entire roof of the cranium in the ox and pig. Facial crest In horses, the ridge on the lateral surface of the face. Facial tuberosity In ruminants, the process on the lateral surface of the face. Cornual process The process of the frontal bone of horned ruminants that is enclosed by the horn. Temporal fossa In ruminants has been pushed to the lateral side of the skull by the frontal bone. Supraorbital foramen Absent in dogs. Foramen orbitorotundum Found in ruminants and pigs, it is the joining of the round and orbital foramina of other species. Rostral bone Unique bone found in the nose of the pig. Bony orbit Complete in the horse and ruminants, is incomplete in the carnivores but is completed by the orbital ligament. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 23 o The Skull of the Dog:  Well-developed facial part  Large orbits (most prominent feature of the lateral view) and temporal fossae  Incomplete postorbital orbits  Prominent tympanic bullae; paracondylar process is conspicuous.  Infraorbital foramen (most prominent feature of the lateral aspect of the face).  **The medial aspect of the bulla meets the occipital bone, and this fusion separates two openings that are confluent in some other species (e.g., horse), namely, the more caudal jugular foramen and the more rostral foramen lacerum.  The nuchal surface is broadly triangular. o The Skull of the Cat:  Globular skull- rounded cranial capsule, short and often weak sagittal crest, convex zygomatic arches, and the relative shortness of the face.  Breed differences- skulls of Siamese have much longer faces, blend smoothly with the cranium without any break (stop) in the dorsal contour; in Persians, the face is short and shallow and the stop is prominent.  Orbits are large, face more directly forward than the dog, and have more complete bony margins (only a small gap in the ovoid margin to be closed by orbital ligament).  Infraorbital foramen is placed close to the rostroventral part of the orbit.  The hard palate is short and wide.  The largest upper P4 is located dangerously close to the orbit (may become involved in a spreading alveolar abscess.  The very large tympanic bulla is so salient (palpable). o The Skull of the Horse:  Characterized by relatively long face (more pronounced in mature than in juveniles; in large than in small breeds).  Cranium is narrow; the external sagittal crest is weaker.  Forehead is wide between the origins of the zygomatic processes of the frontal bone.  Zygomatic arch is conspicuously strong with a complicated articular surface on its caudoventral aspect (rostral tuber, intermediate fossa, and retroarticular process).  Facial crest- a prominent ridge at the rostral portion of the zygomatic arch and runs parallel to the nose and ends in rd th the septum between the 3 and 4 cheek teeth. Nasoincisive notch- separates the pointed nasal bone from the incisive bone. These two landmarks are used as guides to the position of the infraorbital foramen which lies a little caudal to the middle of the connecting line.  Large and very salient paracondylar processes  **Failure of the temporal bone to reach the lateral margin of the occipital bone, which permits the confluence of several foramina (jugular foramen, foramen lacerum, oval foramen) that are distinct in dog.  The tympanic bulla is not prominent; well-marked external occipital protuberance. o The Skull of Bovine:  Relatively short and wide; general form is pyramidal.  Cornual (horn) processes vary greatly in their size and direction (breed, age and sex).  Very wide and flat frontal region bounded by a prominent temporal line.  Principal features of the lateral aspect: confinement of the temporal fossa and elevation of the orbital rima above its surroundings.  There is no facial crest; only the facial tuberosity (for the origin of the rostral part of the masseter).  The temporal and occipital bones are separated by a KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 24 narrow fissure (intermediate between the suture of the dog and the wide opening of the horse and the pig).  Tympanic bulla is prominent and laterally compressed.  The hard palate is long and narrow; no alveoli are present for incisor or canine teeth, which are lacking in the upper jaws of ruminants (dental pad). o The Skull of Pig:  Primitive breeds- more or less pyramidal; improved breeds- sweeps sharply upward to a prominence that rises well above the brain.  Thick nuchal crest and prominent temporal line.  Large paracondylar process and prominent tympanic bullae.  Os rostrale- a small rostral bone in the snout that is set against the end of the nasal septum that gives attachment to the levator labii superioris (muscle concerned primarily with the movement of the snout). THE PARANASAL SINUSES o Cavities or spaces that developed within some of the bones of the skull. o Develop as outgrowths from the nasal cavity and, hence, they all drain directly or indirectly into the nasal cavity. o Communications with the nasal cavity may be divided into two main groups according to their drainage sites: 1. One group draining into the middle nasal meatus 2. The other group draining into the caudal dorsal part of nasal cavity o Six pairs of paranasal sinuses in the horse: 1. Dorsal conchal 2. Ventral conchal 3. Middle conchal a 4. Maxillary 5. Frontal 6. Sphenopalatine a  Largest; it is divided by an oblique septum into rostral and caudal parts. Upper M1, M2 and M3 project into the maxillary sinus. Assignment: Study the TREPHINING Procedure  All the paranasal sinuses directly or indirectly open into the caudal part of the middle nasal meatus via the nasomaxillary orifice or opening.  Boundaries of the maxillary sinus:  Caudal limit- rostral border of the orbit.  Rostral limit- a line from the rostral end of the facial crest to the infraorbital foramen.  Ventral boundary- facial crest.  Dorsal boundary- line from the infraorbital foramen parallel to the facial crest.  Boundaries of the frontal sinus:  Caudal limit- transverse plane through zygomatic process of the frontal bone.  Rostral limit- transverse plane midway between rostral margins of orbit infraorbital foramen.  Medial limit- line 2 cm lateral to dorsal midline.  Lateral limit- line connecting supraorbital foramen with rostral end of medial limit. o Paranasal sinuses of the ox: a 1. Frontal 2. Maxillary 3. Palatine 4. Sphenoidal 5. Lacrimal a  Largest; it is divided into the major caudal frontal sinus and minor rostral frontal sinuses; it presents three diverticula, namely: nuchal, postorbital and corneal.  The maxillary sinus of the ox is undivided (there is no oblique septum). COMMON FORAMINA IN THE SKULL 1. Foramen magnum (occipital bone) - transmits the spinal cord. 2. Hypoglossal foramen/canal (occipital bone) - hypoglossal nerve. 3. Foramen rotundum (basisphenoid) - maxillary nerve. 4. Foramen ovale (basisphenoid) - mandibular nerve (horse and pig). 5. Foramen alare caudale (basisphenoid) - maxillary artery. KHAN L. JUNATAS, DVM| Department of Basic Vet Sci, CVM-USM  Comparative Veterinary Macroscopic Anatomy 25 6. Foramen alare rostrale (basisphenoid) - maxillary artery and maxillary nerve. 7. Foramen stylomastoideum (temporal bone) - facial nerve. 8. Foramen supraorbitale (maxilla) - supraorbital vein. 9. Foramen infraorbitale (maxilla) - maxillary artery, vein and nerve (a, v, n). 10. Foramen maxillare (maxilla) - maxill