BIO 415L: Feline Skeletal System

• Felis domestica is dissected in BIO 415L.

Skeletal System

• The skeletal system includes the frontal, nasal, and maxilla bones, which are all part of the skull.
• The zygomatic and parietal bones are also part of the skull.
• The squamosal and occipital bones, as well as the foramen magnum, are cranial structures.
• The atlas, axis, and cervical vertebrae form the neck.
• The scapula, clavicle, humerus, radius, and ulna comprise the forelimb.
• The manus is the paw, and the thoracic vertebrae make up the back.
• The dorsal and transverse processes are part of the vertebrae.
• The lumbar vertebrae are found in the lower back.
• The sacrum connects the spine to the pelvis.
• The caudal vertebrae form the tail.
• The ribs and costal cartilage protect the thorax.
• The sternum is the breastbone.
• The femur, patella, tibia, and fibula comprise the hindlimb.
• The pes is the foot, and the mandible is the jaw.
• Incisors, canines, premolars, and molars are teeth.

Mammalian Dentition

• All mammals have four groups of teeth with different functions.
• The number of teeth may be reduced in groups with specialized diets, such as cats.

Feline Dentition

• Cats are hypercarnivores, eating only meat.
• Hypercarnivory results in a shortened snout, increasing bite force on canine teeth, a loss of grinding molars, and a reduction in total tooth count.
• The carnassial teeth, the last upper premolar and first lower molar, are a synapomorphy of Carnivora.
• Carnassial teeth slice through meat and fit together like meat scissors.

Tooth Types

• Incisors are in the premaxillae, three in each, and groom the cat's fur.
• The canine is large, curved, and the first tooth in the maxilla.
• The diastema, or gap, is located between the canine and the small peg-like P2 and resulted from the loss of P1.

Premolars and Molars

• Premolars 2 through 4 (P2-P4) are phylogenetically represented by the teeth.
• P3 is a larger, triangular tooth in front of the long blade-like P4.
• Blade-like P4 is the main meat-shearing tooth, also known as the carnassial, meeting blade-like m1, the carnassial of the lower jaw.
• Molars are small, final teeth, located in lateral view by P4's posterior end.
• The cat dental formula is 3,1,3,1 / 3,1,2,1.

Cat Skeletal Anatomy

• Week 1 involves skeletal and external anatomy, submission of a labeled digital skull.
• Week 2 focuses on musculature, and submission of a muscle dissection photo.
• Week 3 involves internal anatomy, and submission of an internal dissection photo and checklist.
• All of the cat materials, photos, etc., are due April 2nd to Halo.

Skeletal Terminology

• A condyle is a large prominence that often provides structural support via hyaline cartilage, such as the occipital condyle.
• An epicondyle is a prominence on top of a condyle that attaches muscle and connective tissue to bone, such as the medial and lateral epicondyles.
• A crest is a raised or prominent part of the edge of a bone, such as the iliac crest.
• A facet is a smooth, flat surface that forms a joint with another flat bone or facet, creating a gliding joint, i.e., the vertebrae.
• A fissure is an open slit in a bone, usually housing nerves and blood vessels.
• A foramen is a hole through which nerves and blood vessels pass, i.e., the foramen magnum.
• A fossa is a shallow depression in the bone surface.
• A meatus is a tube-like channel that extends within the bone, may provide passage and protection to nerves, vessels, and even sound. "External acoustic meatus" is an example.

Skull Anatomy

• The temporal fossa protects the temporal and parietal lobes of the brain, posterior to the orbit.
• It originates from the Temporalis M, which closes the jaw.
• The temporal fossa is subdivided into squamosal, mastoid, petrosal, ectotympanic, and endotympanic regions.
• The frontal bone forms the dorsal and lateral surfaces of the skull posterior to the nasals, laterally forming most orbital walls.
• Nasal bones are anteriorly located, small, and triangular.
• The maxilla holds teeth, with the hard palate ventrally.
• First in the maxilla is a large, curved canine tooth, followed by three premolars.
• The zygomatic bone forms the zygomatic arch, with a shelf forming the anterior floor of the orbit.
• The infraorbital canal is a large passage within the maxilla, with the anterior end of the zygomatic arch.
• Parietal bone forms the dorsal and lateral parts of the cranium, with a small interparietal between the posterior ends of the parietals.
• In the skulls of older individuals, the interparietal fuses to the surrounding bones.
• The squamosal bone is a large, flat, thin scale-like bone ventral to the parietals that completes the lateral wall of the braincase.
• It helps form the zygomatic process, that extends laterally and then anteriorly to form the posterior part of the zygomatic arch.
• The occipital bone forms the occiput and skull's posterior surface and contributes to the basicranium.
• The foramen magnum is passage for the spinal cord and pierces the posterior surface of the skull (occiput).

Mandible Details

• The mandible is the lower jaw, consisting of single dentary bones forming the mandible.
• The mandibular symphysis is the anterior articulation point.
• The body is where teeth implant, at the dentary's horizontal part.
• The ascending ramus is posterior to the body.
• The coronoid process is largest, extending dorsally and inserted mainly into its dorsolateral and medial surfaces by the temporal muscle.
• The masseteric fossa is a large, triangular depression on the lateral surface of the coronoid process and an insertion area part of the masseteric musculature.
• The condyloid process forms the lower half of the temporomandibular joint.
• The condyloid process bears a semicylindrical facet for articulation with the mandibular fossa on the temporal bone.
• The joint located in the condyloid process permits mainly up and down (or orthal) movements of the jaw and restricts lateral motion.
• A roughened area is located on the anteromedial surface of the condyloid process, the insertion site for the medial pterygoid muscle.
• The medial surface of the condyloid process serves as the insertion site for the lateral pterygoid muscle, and its lateral surface aids the masseteric musculature.

Skull Practice

• Three-dimensional models of cat skulls can be found online.
• Mountain lion: https://sketchfab.com/3d-models/puma-concolor-coryi-uf-m-29532-skull-a7110e603c59444c896c431463cb6560.
• Clouded leopard: https://sketchfab.com/3d-models/clouded-leopard-skull-and-mandible-uf-26153-7c059f4cc4374d27bb08b8b987c78a8b.
• Waterbuck skull: https://sketchfab.com/3d-models/waterbuck-skull-dc2abd4f5f5c4f4cb9f90407cfcbf916, where you can label the frontal, nasal, maxilla, zygomatic, parietal, squamosal, and occipital bones, as well as the foramen magnum.

Hyoid Bone

• The hyoid bone sits in the throat, providing support for the tongue and larynx.
• Smaller, purring cats tend to have rigid hyoid bones.
• Bigger cats have flexible, less bony hyoids that let them roar and keep them from purring.

Postcranial Anatomy

• Follow along with the lecture by looking at a whole-body scan of a small marsupial (mulgara), online at https://sketchfab.com/3d-models/dasycercus-cristicauda-ypm-15882-01e6659feb0b491d8048fae0e338a453.

Cervical Vertebrae Characteristics

• Cervical vertebrae have 7 bones (C1 - C7).
• The first two are specialized to support head movement.

Atlas and Axis

• The atlas as the first vertebra (C1), named after the mythological giant Atlas, has ring-like with lacking a neural process but a prominent neural arch.
• Transverse processes are broad and wing-like.
• The axis is the second cervical vertebra (C2).
• The axis joints allow mainly rotational movements of the head.

Thoracic Vertebrae

• The neural process is a bony projection off the posterior (back) of each vertebra.
• The neural process protrudes to the laminae of the vertebral arch joint
• The transverse processes are broad and wing-like.
• Usually, there are 13 thoracic vertebrae, while humans have 12, with additional facets to allow articulation.
• The capitulum of a rib sits between and articulates with two successive centra, at the costal demifacets.
• Each costal facet's ventral surface articulates with the tuberculum of the corresponding rib.

Posterior Changes in Thoracic Vertebrae

• The "first" thoracic vertebra has paired costal facets anteriorly and paired demifacets posteriorly.
• The "last few" thoracic vertebrae (usually the 11th through 13th) only have paired costal facets on the centrum, i.e., no demifacets.
• The 11th thoracic has a markedly reduced transverse process, while the 12th and 13th "lack" transverse processes, reflecting the absence of a tuberculum on the last few ribs.
• Last few thoracic vertebrae have a slender accessory process.

Lumbar Vertebrae

• Typically, there are seven lumbar vertebrae.
• Characterized by their large size and increase in size posteriorly through the lumbar series.
• Pleurapophyses are elongated, blade-like processes that sweep anteroventrally.
• Accessory processes are present except for last two lumbar vertebrae, with pre-zygapophyses which are extended dorsally.
• Attachment for epaxial muscles occurs here.

Sacrum Characteristics

• The sacrum is a single structure fused from three sacral vertebrae.
• The sacrum links spine to the pelvic girdle and anteriorly articulates with pelvis, with size decreasing posteriorly. Three neural processes are part of the sacrum.
• The sacrum contains two pairs of sacral foramina on the dorsal and ventral surfaces and creates passage for the dorsal branches of spinal nerves.
• The pleurapophysis of the first sacral forms most of the articular surface for the pelvis.

Caudal Vertebrae

• There are 21 to 23 caudal vertebrae, the smallest of the vertebral column.
• They progressively become smaller and less complex posteriorly, with more posterior caudal vertebrae elongated, cylindrical structures consisting almost entirely of the centrum.
• Hemal arches are the presence of small V-shaped bones on the anterior end of the ventral surface of the vertebra.
• Successive hemal arches enclose a hemal canal through which caudal blood vessels pass.
• Each hemal arch articulates with a pair of small tubercles, the hemal processes, on the centrum. NOTE: The small, delicate arches are usually lost during preparation, but their position can be determined by identifying the hemal processes.

Ribs and Costal Cartilage

• Ribs are a cage that is strong and part flexible and protects vital organs and participates in inspiration and expiration.
• The ribs differ in length but are generally similar in being curved, slender and are rod-like bones
• Each rib articulates dorsally with the vertebral column and ventrally with a costal cartilage.

Sternum

• The sternum is the chest's ventral-most bone.
• There are 9 true vertebrosternal ribs in which each costal cartilage attaches directly to the sternum.
• There are 3 false vertebrochondral ribs in which each costal cartilage attaches to the costal cartilage of another rib and does not attach directly to the sternum.
• Floating ribs are last and have a vertebral rib, with short cartilage not gaining access to the sternum and considered to be a 'false' rib.

Cat Forelimb Anatomy (Felidae)

• Forelimbs are flexible and muscular, so they can grapple and restrain with agility, thus very useful for climbing trees.
• The claws are digitigrade (AKA walks on tippy toes) and retractable, allowing for enhanced sharpness and assisted climbing.
• The pectoral girdle is the clavicle bone, in which the bone is small, slender, and slightly curved but does not articulate with other skeletal elements; it is the anterior of the proximal end of the humerus.
• The scapula is shoulder blade which is flat and triangular with a medial cartilage that is nearly flat and has a lateral prominent scalpel spine, therefore its apex directs ventrally.
• There is loss of ossification because the cats are highly flexible.

Scapula Details

• The Coracoid process projects medially from the anterior margin of glenoid fossa.
• It bears a medial subscapular fossa in that it is relatively flat, with slight scar ridges to indicate muscular insertions.

Humerus

• The humerus is the bone of the brachium, or proximal part of the forelimb, proximally articulating glenoid fossa of the scapula and distally with the radius and ulna.
• Anteriorly between the tuberosities, there is bicipital groove which passes the tendon of biceps brachii
• The pectoral ridge is extended from the greater tuberosity of the anterior, humeral shaft.
• A less prominent deltoid ridge extends from the posterior part of humerus.

Ulna

• The ulna is one of the two bones and is the longer of the two, being within the forearm, the antebrachium.
• The prominent portion that it bears is the shaft which tapers distally and proximally articulates with the humerus and radius along with carpus and the wrist and the trochlear notch or semi-circular area which articulates with trochlea of the humerus.
• Olecranon has insertion site for triceps muscle extending process which creates trochlear notch.
• The radial notch articulates with head of the radius. The processes taper, giving way and ending in styloid.

Radius

• The radius is the second bone, found within the antebrachium.
• The radius is slender proximally and widened distally and articulates with the lateral part of the humerus and the medial part of the carpus.
• Proximally it consists of the head, which creates an oval, concave fovea that articulates the capitulum of the humerus.
• The neck of the radius is short and is where the biceps muscle inserts.

Manus Characteristics

• Manus contains three portions: the carpus (wrist), metacarpus, and the phalanges.
• Cats have five digits, each formed from phalanges where 7 irregularities form 2 shaped-groups of small bone that makes carpus.

Manus and Claw Anatomy

• At rest, claws are retracted, or hidden with fur in which each contract with muscles of the toe to make distal phalanx forward, exposing those claws.
• Flexible wrist can be rotated to the sole of the manus faces, upward = supination.

Pelvic Girdle

• The hind limb contains a hip which pairs bone around that hip itself and articulate on where all the bones ventrally come together to the pelvic symphysis along dorsal sacrum too.

Hind Limb Details (Femur)

The femur is located in the proximal aspect of the thigh.

• The head contains a hemispherical shape which articulates with acetabulum, and the roughened part that's lateral to that is where greater trochanter attachment for hip moves from along musculature from there.
• From the shaft lies musculature insert site to allow better muscular insertions.
• The patella is a tear-shaped sesamoid bone in which apex directs distally, anterior surface is roughened and the posterior has shallow concave structure for articulation against that of this hip.
• The tibia is one of the middle parts this area where lateral sides bare condyles and where bone connects, and there's tibula shafting too.
• The tibula and all related triangular structures are faced posterolateraly while that of tibia faces distal and laterally.

Hind Limb Fibula and Pes

• The tibia, which lies more the most part, has two shafts that widen toward and articulate around more distal section. The hind limb connects where condyles are to move leg or shift it but when that goes down tibia starts there too where you can see these shafts with distal facets.
• Also pes has two larger sized bones.
• Digitgrade orientation.
• Animals can walk on toes.
• Allows for greater economy with running.
• And energy usage is much safer from those ligaments to other joints (foundation).

External Anatomy Terms

• Pinna=ear flaps
• Palpebrae=eyelids
• Nares= nostrils
• Vibrassiae=whiskers
• Carpal and tarsal pads
• Head and trunk are separated by a distinct neck

External Anatomy Terms on the Dorsum

• Dorsum are trunkis that cover dorsal parts of the body.
• Thorax are ventral which divided into thorax to abdominal regions of each animal during that moment with where hind limb is the limb which tail can connect.

Cat Dissection: Muscular System

• The muscular system of the domestic cat (Felis domestica) will be dissected.
• The presentation is by Dr. Polekoff.

Muscular System Entities

• Includes the:
  • Parotid & Mandibular salivary gland
  • Temporalis m.
  • Masseter m.
  • Digastric m.
  • External jugular v.
  • Clavotrapezius m.
  • Clavobrachialis m.
  • Sternohyoid m.
  • Sternomastoid m.
  • Acromiotrapezius m.
  • Spinodeltoid m.
  • Lateral & long head of triceps brachii mm.
  • Pectoralis major m.
  • Pectoralis minor m.
  • Latissimus dorsi m.
  • Lumbodorsal fascia
  • Pectoantebrachialis m.
  • External oblique m.
  • Internal oblique m.
  • Transverse abdominis m.
  • Rectus abdominis m.
  • External oblique aponeurosis
  • Linea alba
  • Xiphihumeralis m.
  • Biceps femoris m.
  • Semitendinosus m.
  • Semimembranosus m.
  • Sartorius m.
  • Tensor fasciae latae
  • Fascia lata
  • Gluteus medius m.
  • Gluteus superficialis m.

Muscle Terminology: Naming

• Muscles are named based on multiple factors: origin, insertion, position, action, shape, and form.
• Area of Origin and Insertion: Muscle's area of origin and area of insertion.
  • Spino-deltoid extends from the spine of the scapula to the deltoid ridge of the humerus.
  • Sterno-mastoid extends from the sternum to the mastoid process of the temporal bone of the skull.
  • Xiphi-humeralis extends from the xiphoid process of the sternum to the humerus.
• Main position of a muscle
  • Subscapularis occupies the subscapular fossa of the scapula
  • Temporalis occupies the temporal fossa of the skull.
• Descriptors of action as well as shape and form.
  • Adductor femoris adducts the femur or thigh.

Movement

• Flexion
  • Decreases the angle of the joint.
  • Brings two bones closer together.
  • Typical of hinge joints like knee and elbow.
• Extension
  • Opposite of flexion.
  • Increases the angle between two bones.
• Hyperextension
  • Angle between two bones > 180°.
• Abduction
  • Movement of a limb away from the midline.
• Adduction
  • Movement of a limb toward the midline.
  • Opposite of abduction.
• Circumduction
  • Combination of flexion, extension, abduction, and adduction.
  • Common in ball-and-socket joints.
• Supination (think soup)
  • Lateral Rotation of forearm.
  • Palm facing anterior/superior.
• Pronation
  • Medial rotation of forearm.
  • Palm facing posterior/inferior.

Head and Forelimb Muscles

• Parotid & Mandibular Gland
  • Largest and most important salivary glands.
• Temporalis M.
  • Jaw-closing muscle.
  • Lateral surface of the cranium.
  • Arises from the temporal fossa.
  • Deep to the parotid and mandibular glands.
• Masseter M.
  • Jaw-closing muscle.
  • Larger muscles covering the posterolateral surface of the jaw.
• External Jugular V.
  • Brings blood back from head and neck.
  • Joins the smaller internal jugular vein to form the bijugular trunk.
• Digastric M.
  • Depresses mandible.
  • Important for chewing and swallowing.
  • Anterior to the transverse jugular vein.
  • Triangular area with sides of the triangle formed by the digastric muscles.
  • Medial edges of the dentary.
  • Converge at mandibular symphysis.
• Mylohyoid
  • Lies between
  • Muscle that elevates the tongue/hyoid

Jaw Muscles

• Both the temporalis and masseter muscles are involved with closing the jaw, they concentrate force in different areas.
  • Temporalis originates at the temporal fossa and inserts at the coronoid process of mandible.
  • Masseter originates at the zygomatic arch and inserts at the ventral part of the masseteric fossa of mandible.
• Digastric muscle opens the jaw and is comparatively smaller.
• Which jaw muscle plays a role in bite force at the canines is a group activity.
• View how the temporalis and masseter muscles fit into the pteropus giganteus (bat) skull
• Draw those two muscles onto waterbuck and clouded leopard skulls for group activity
  • Which muscle is larger in the waterbuck skull (top)?
  • Which muscle is larger in the clouded leopard skull (bottom)?

Head and Forelimb: Shoulder Muscles

• Acromiotrapezius M.
  • It is wider, but very thin.
  • Fans out and inserts along the scapular spine.
  • Adducts and stabilizes scapula >>> toward the dorsal midline
• Spinodeltoid M.
  • Flexes and laterally rotates humerus
  • Extends anteroventrally from the scapular spine
  • Insertion of the acromiotrapezius.
• Clavotrapezius M.
  • Pulls the scapula anterodorsally
  • Covers neck laterally, originates from the neck middorsally
  • Extending from just behind the skull to the acromiotrapezius
  • NOTE: In mammals with a well-developed clavicle, the clavotrapezius inserts on the clavicle. In cats fibers instead insert into the clavobrachialis which appear to be continuous.
• Clavobrachialis M.
  • Flexes antebrachium
  • Insert on the ulna.
  • NOTE: The clavicle is embedded in the musculature but may be discerned by palpation.
• Latissimus Dorsi M.
  • Pulls the humerus posterodorsally
  • Is a wide muscle
  • Originates mainly from the lateral margin of lumbodorsal fascia
  • Attaches anteroventrally and converge toward the axillary region (armpit)
• Lumbodorsal Fascia
  • Large, white covering on back in the lumbar region
  • Composed of two main sheets of tough connective tissue
  • Equivalent to Thoracolumbar fascia in humans

Trunk and Forelimb: Upper Arm and Chest Muscles

• Lateral & Long Head of Triceps Brachii Mm.
  • Extend antebrachium.
  • Long head covers the brachium posteriorly
  • Lateral head covers the brachium laterally.
  • Insert on the olecranon process of ulna by a common tendon.
• Pectoantebrachialis M.
  • Adducts humerus
  • Most superficial muscle
  • Thin, narrow, anterior muscle that extends laterally.
• Pectoralis Major M.
  • Adducts humerus.
  • Inserts into the pectoral ridge on the humerus
• Pectoralis Minor M.
  • Adducts humerus
  • Inserts into the pectoral ridge on the humerus
  • Lying dorsal and posterior to the pectoralis major
  • Names are derived from human terminology, in which the pectoralis major is indeed larger.
• Abdominal Wall Muscles
  • Constrict the abdomen.
  • External Oblique = most superficial layer
  • Internal Oblique = Middle layer
  • Transverseus Abdominis = deep layer
  • Rectus Abdominus = fourth muscle.
  • Draw the ribs and sternum posteriorly, flexing the trunk
  • Compresses abdomen
• What function would adduction serve in birds and cats during a group activity.
• External Oblique Aponeurosis
  • External oblique attaches through aponeurosis midventrally
  • Covers the deeper musculature of the ventral surface of the abdomen
• Linea Alba
  • Latin for "white line"
  • Midline fibrous line in the anterior abdominal wall
  • Formed by the median fusion of the layers of the rectus sheath
  • Insertion for external intercostals, internal oblique, and transversus abdominis

Hindlimb

• Tensor Fascide Latae and Fascia Lata
  • Contribute to flexing of the thigh
  • Originates from the anteroventral surface of ileum
• Tensor Fasciae Latae M. fans out distally and inserts on the fascia lata
• The Tensor fasciae latae are Subdivided into longer anterior and triangular posterior portions
• Fascia lata us a tough membrane which extends to the knee joint
• Biceps Femoris
  • Flexes crus
  • Extends + Abducts thigh
  • Originate from the ischial tuberosity
  • Most conspicuous muscle of the thigh
  • Insert on the patella and the proximal portion the tibia
• Sartorius M.
  • Extension of crus and Adducts thigh
  • Lies along the anterior edge of thigh

Hindlimb: Dorsal View

• Gluteus Medius vs Gluteus Superficialis
  • Originates at the sacral and caudal vertebrae
  • Also abduct the thigh.

Hindlimb: Ventral View

• Semitendinosus vs Semimembranosus
  • Flexes the crus and Extends the thigh

Hamstring Muscles

• Side Note: The semitendinosus, semimembranosus and biceps femoris comprise the hamstring muscle grouped (RODGERS & RAJA, 2022)

Skinning

• When you skin the trunk, notice the thin and narrow bands of muscles that adhere to the underside of the skin.
• These bundles represent the cutaneous maximus, one of the cutaneous muscles, a large sheet that covers much of the trunk and is especially prominent ventrally and near the axilla (armpit).
• This muscle should be removed with the skin, except near the axilla since In this region, it adheres strongly to the shoulder muscles and should be cut.

Internal Organs

• The internal organs system includes the:
  • Thyroid cartilage
  • Cricoid cartilage
  • Thyroid gland
  • Trachea
  • Common carotid a.
  • Anterior vena cava
  • Posterior vena cava
  • Thymus
  • Pericardium
  • Heart (remove to observe chambers)
  • Diaphragm
  • Right lung lobes (anterior, middle, posterior, accessory)
  • Left lung lobes (anterior, middle, posterior)
  • Diaphragm
  • Round ligament
  • Liver right lateral lobe
  • Liver right medial lobe
  • Liver caudate lobe
  • Liver quadrate lobe
  • Liver left lateral lobe
  • Gall bladder
  • Stomach
  • Spleen
  • Pancreas
  • Omentum
  • Small intestine (duodenum, jejunum, ileum)
  • Ileocecal junction
  • Large intestine (ascending, transverse, descending colon)
  • Rectum
  • Urinary bladder
  • Abdominal aorta
  • Posterior vena cava
  • Kidney
  • Renal a. & v.
  • Adrenal gland
  • Ureters
  • Bladder
  • Fat pad
  • Penis (male)
  • Testes (male)
  • Epididymis (male)
  • Pampiniform plexus (male)
  • Prostate gland (male)
  • Ovary (female)
  • Uterine horn (female)
  • Body of uterus (female)
  • Cervix (female)
  • Vagina (female)

Ventral Throat Region

• The following are located in the ventral throat region:
  • Parotid gland
  • Zygomatic arch
  • Dorsal buccal branch of facial n.
  • Masseter
  • Parotid duct
  • Sublingual gland
  • Molar gland
  • Mandible
  • Ventral buccal branch of facial n.
  • Digastric
  • Linguofacial v.
  • Sternohyoid
  • Transverse jugular v.
  • Lymph node
  • Clavotrapezius
  • Maxillary v.
  • Mandibular duct
  • Mandibular gland
  • Lymph node (cut)
  • Sternomastoid
  • External jugular v

Nasal Conchae (Turbinates)

• Nasal conchae are curved, labyrinth-like bones that filter air coming in through the nose before it enters the trachea.
  • They heat and humidify incoming air.
  • They trap particles (in mucus).
• Complex turbinates are associated with high metabolic rate and endothermy.

Larynx

• The larynx is a chamber at the anterior end of the trachea or windpipe.
• The glottis is the opening into the larynx.
  • It is guarded by the epiglottis, a plough-like, cartilaginous structure at the base of the tongue.
• The epiglottis is supported by an epiglottal cartilage.
  • The epiglottis flips back to cover the glottis during swallowing.
  • This helps food pass posteriorly through the laryngopharynx and into the esophagus.

Trachea

• The trachea has c-shaped tracheal cartilages
  • The cartilages dorsally incomplete.
  • The incomplete cartilages keep the trachea open.
• The esophagus lies dorsal to the trachea.

Pericardium

• The pericardium is a membrane enclosing the heart.
  • It has an outer fibrous layer and an inner double layer of serous membrane.
• It provides mechanical protection for the heart and big vessels.
• Mesothelial cells create a non-adhesive, slippery, protective surface.
  • The pericardium is important in all aspects of pericardial function and lubrication, which reduces friction between the heart and surrounding structures.

Heart and Diaphragm

• The heart lies within the pericardial cavity, which is isolated from the mediastinum by the pericardium; remove the heart to observe the chambers.
• The diaphragm is a thin skeletal muscle at the base of the chest that separates the abdomen from the chest.

Tidal Ventilation

• The diaphragm is used for tidal ventilation in mammals.
  • Inhaling involves contracting and flattening the diaphragm, creating a vacuum effect that pulls air into the lungs.
  • Exhaling involves relaxing the diaphragm, pushing air out of the lungs.

Lung Lobes

• There are 4 right lung lobes, including the anterior, middle, posterior, and accessory lobes.
• There are 3 left lung lobes, including the anterior, middle, and posterior lobes.

Vessels

• Oxygen depleted blood returns to the right atrium through the anterior and posterior vena cavae, then it gets pumped to the right ventricle, then through the pulmonary arteries to the lungs for reoxygenation.
  • The anterior vena cava drains the region anterior to the diaphragm.
  • The posterior vena cava drains the region posterior to the diaphragm.

Blood Flow Through the Heart

• Blood enters the right side of the heart via the vena cava.
• Blood exits the heart and goes to the lungs via the pulmonary arteries.
• Blood re-enters the left side of the heart via the pulmonary veins.
• The left ventricle pumps blood from the aorta to the body.

Abdominal Aorta

• The abdominal aorta is the main blood vessel in the abdominal cavity. -It transmits oxygenated blood from the thoracic cavity to organs within the abdomen and to the lower limbs.

Thymus

• The thymus is a lymphoid organ especially important in the development of the immune system.
  • T lymphocytes mature and proliferate in the thymus.
  • The thymus is especially prominent in young mammals.

Liver

• Liver lobes are covered by visceral peritoneum.
  • The falciform ligament, an example of ventral mesentery, passes from the diaphragm to the liver and separates the liver into left and right halves; the falciform ligament may be hard to distinguish in overweight cats because it is very fatty.
• All of the blood leaving the stomach and intestines passes through the liver.
  • The liver processes the blood, breaking it down, balancing it, and creating nutrients, and also metabolizes drugs into forms that are easier to use or nontoxic.
• The liver has five lobes:
  • Right lateral lobe
  • Right medial lobe
  • Caudate lobe
  • Quadrate lobe
  • Left lateral lobe

Gallbladder

• The main function of the gall bladder is to store bile.
  • Bile helps the digestive system break down fats.

Stomach

• The stomach is a large, light-colored, sac-like organ partially exposed posterior to the left lateral lobe of the liver.
• The pyloric sphincter is distally oriented toward the right; the stomach constricts here at into the pyloric sphincter.
  • The pyloric sphincter is a muscular, valve-like separation between the stomach and the duodenum.
  • The inside walls of the stomach have folds called rugae.

Omentum

• The omentum is a large flat adipose tissue layer nestling on the surface of the intra-peritoneal organs.
  • It contains biological properties including neovascularization, haemostasis, tissue healing, and regeneration.
• The abdominopelvic cavity is covered ventrally by the omental bursa.
• The omental bursa:
  • Large, double-layered, fat-laced mesentery covers the intestines like an apron.
  • The omentum extends posteriorly to the urinary bladder.

Pancreas

• The pancreas consists of endocrine and exocrine glandular tissue.
  • Exocrine glands secrete substances into a ductal system to an epithelial surface.
  • Endocrine glands secrete products directly into the bloodstream.
    • The exocrine portion of the pancreas makes up the larger part.
    • The endocrine portion consists of small pockets of tissue
      • Beta cells = insulin
      • Alpha cells = glucagon
• Two ducts carry exocrine secretion to the duodenum.
• Pancreatic enzymes break down sugars, fats, and starches.
• Also makes hormones or chemical messengers that travel through blood.
• The main pancreatic duct passes, together with the bile duct, to the duodenum.

Spleen

• The spleen is a large, dark organ to the left of the stomach.
  • It fights invading germs in the blood.
  • It contains infection-fighting white blood cells.
  • It controls the level of blood cells, white blood cells, red blood cells and platelets.
  • It filters the blood and removes any old or damaged red blood cells.

Small Intestine (Duodenum, Jejunum, Ileum)

• It fills nearly all of the abdominopelvic cavity posterior to the liver and stomach.
• It is subdivided