SUPERFICIAL MUSCLES OF THE FACE
- Function to open, close, or move the lips, eyelids, nose, and ear
- Platysma m.
 Cutaneous muscle that extends from the dorsal media raphe of the neck to the angle of the mouth
 At the labial commissures, blends with the orbicularis oris m., buccinator m., and zygomaticus m.
 Innervated by the cervical, buccal and caudal auricular branches of CN VII
 Involved in behavioral facial expression (pulls labial commissures caudally)
Clinical note: The platysma m. does not normally play a role in twitching of the skin over the neck and face (as does the
cutaneous trunci m.). Involuntary contraction of the platysma that results in twitching of skin on the dorsolateral aspect of
the neck may be caused by chronic middle ear infections involving CN VII irritation.
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Sphincter colli profundus m.
 Pars palpebralis
o Attaches along the lower eyelid, coursing over the buccinator m. and rostral zygomaticus m.
 Pars intermedia (extends ventrally from scutiform cartilage, over the masseter m.)
 Innervated by the cervical n. of CN VII
Frontalis m.
 Thin muscle covering the temporalis m.
 Rostrally blends with the deep fascia of the upper eyelid extending to the orbital ligament
 May function to move the ear dorsorostrally and aid in elevating the upper eyelid
Parotidoauricularis m.
 Lies on the lateral surface of the parotid salivary gland
 Innervated by the cervical n. of CN VII
MUSCLES OF THE LIPS, NOSE AND CHEEK
- Zygomaticus m.
 Strap-like muscle extending from the scutiform cartilage to the lateral angle of the mouth
 Helps draw the angle of the mouth caudally
 Innervated by the buccal nn. of CN VII
- Orbicularis oris m.
 Lies within the lips, circling both superior and inferior labia
 Functions to close the mouth and pull the nose ventrally (aids in sniffing)
- Levator nasolabialis m.
 Thin, flat muscle located over the lateral aspect of the nasal and maxillary bones
 Attaches on the upper lip and lateral nasal ala
 Innervated by the palpebral n. branch of the auriculopalpebral n. of CN VII
 Functions to elevate the lips (snarling) and dilate the nostril
- Levator labii superioris m.
 Small muscle located medial to the levator nasolabialis m.
 Arises from the maxilla along the lateral and inferior borders of the infraorbital foramen
- Caninus m.
 Originates along the ventral rim of the infraorbital foramen and continues rostrally into the upper lip
 It functions to dilate the nostril and elevate the upper lip near the incisor and canine teeth (snarling)
- Mentalis m. (small muscle attaching to the lower lip ventral to the corner incisor to the body of the mandible)
- Buccinator m. (only cheek muscle)
 Attaches to the alveolar margins of the mandible and maxilla
 Innervated by the buccal nn. of CN VII
 Aids in chewing by pushing food from the buccal vestibule towards the teeth
Clinical note: Damage to the buccal branches of CN VII results in paralysis of the buccinator m. This is a serious condition resulting
in the accumulation of a food bolus in the buccal vestibule, causing chronic irritation and necrosis of the buccal mucous membrane.
MUSCLES OF THE EYELIDS
- Orbicularis oculi m.
 Weak sphincter muscle of the eyelid that originates from the medial orbital ligament, radiates onto the
superior and inferior palpebrae, meeting again at the lateral canthus
 Innervated by the palpebral branch of the auriculopalpebral n. of CN VII
 Aids in closing the eyelids
- Retractor anguli oculi lateralis m.
 Considered part of the frontalis m.
 Attaches from the lateral palpebral angle to the temporal fascia over the zygomatic arch
 Innervated by the palpebral branch of the auriculopalpebral n. of CN VII
 Aids in closing the eyelids
MUSCLES OF MASTICATION and related muscles
- Temporalis m.
 Largest and most powerful masticatory muscle in carnivores
 Arises from the temporal fossa and insert on the coronoid process of the mandible
 A well-defined fibrous septum is located in the middle of the muscle to increase SA for attachment
 Innervated by the CN V3 (mandibular branch)
 Closes the mouth
- Masseter m.
 Second largest muscle of the head
 Attaches along the zygomatic arch and occupies masseteric fossa (lateral surface of mandibular ramus)
 Innervated by the masseteric n. of CN V3
 Closes the mouth
Clinical note: Masticatory muscle myositis is an inflammatory condition primarily affecting temporalis and masseter mm.
Masticatory muscle involvement may indicate an autoimmune reaction targeting specific myofibrillar proteins.
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Digastricus m.
 Arises from the paracondylar process of the occipital bone and inserts on the caudoventral mandible
 Does not grossly exhibit two bellies, though developmentally derived from two branchial arches
o Rostral part is innervated by CN V3
o Caudal part is innervated by CN VII
 Only muscle that can open the mouth
o Paralysis of left and right digastricus mm. will result in a closed-mouthed locked jaw
 Facial a. courses between ventral margin of the masseter m. and dorsal margin of digastricus m.
Medial pterygoid m.
 Large muscle arising from the pterygopalatine fossa formed by the maxilla, palatine, zygomatic,
pterygoid, and sphenoid bones
 Innervated by CN V3
 Closes the mouth and assists in chewing
Lateral pterygoid m.
 Small muscle extending from the pterygopalatine fossa to the medial aspect of the mandibular condyle
 Innervated by CN V3
 Closes the mouth and protrudes the mandible
SUPERFICIAL STRUCTURES OF THE EYE
- Superior palpebra (upper eyelid)
 Cilia (eyelashes) only found on the superior palpebra
- Inferior palpebra (lower eyelid)
- Lateral palpebral commissure
 Intersection of the superior and inferior palpebrae on the lateral aspect
 Attached to the zygomatic bone via the poorly-developed lateral palpebral ligament
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Medial palpebral commissure
 Intersection of the superior and inferior palpebrae on the medial aspect
 Attached to the frontal bone via the well-developed medial palpebral ligament
Palpebral conjunctiva
 Mucous membrane that covers the inner surfaces of the eyelids
Bulbar conjunctiva
 Mucous membrane that reflects from the palpebral conjunctiva to cover the globe of the eye
 Angle of reflection of the palpebral mucous membrane is called the fornix
 Potential cavity formed is called the conjunctival sac
Lacrimal caruncle (triangular prominence of finely-haired skin at the medial commissure)
Lacrimal gland (lies on the medial side of the orbital ligament within the periorbita)
Plica semilunaris (third eyelid)
 Concave fold of the palpebral conjunctiva and cartilage that protrudes from the medial angle of the eye
 Surrounded by a body of fat and glandular tissue called the superficial gland of the third eyelid
EXTRAOCULAR MUSCLES, NERVES, and VESSELS
The orbit is a conical cavity containing the eyeball and ocular adnexa. The orbits is framed laterally by the frontal,
lacrimal, maxillary and zygomatic bones and orbital ligament, medially by parts of the frontal, presphenoid, and
lacrimal bones, dorsally by the temporalis m., and ventrally by the zygomatic salivary gland and pterygoid mm.
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Orbital ligament
 Completes and forms the lateral margin of the orbit
 Extends from the frontal process of the zygomatic bone to the zygomatic process of the frontal bone
 Not present in animals that have a more complete bony orbit (due to longer bony processes)
Levator palpebrae superioris m.
 Originates at the apex of the orbit and inserts as a flat tendon in the superior palpebra (upper eyelid)
 Innervated by CN III
Periorbita of the eye is composed of CT and smooth muscle and contains the 7 striated, extraocular muscles
along with their vessels and nerves. These muscles all insert on the fibrous coat of the eyeball
 Dorsal rectus m.
o Innervated by CN III
 Ventral rectus m.
o Innervated by CN III
 Medial rectus m.
o Innervated by CN III
 Lateral rectus m.
o Innervated by CN VI
 Dorsal oblique m.
o Arises from the dorsomedial margin of the optic canal, courses over a small cartilagenous
trochlea, and inserts onto the sclera under the tendon of insertion of the dorsal rectus m.
o Innervated by CN IV
 Ventral oblique m.
o Arises from the palatine bone on the medial aspect of the body orbit
 Retractor bulbi m.
o Consists of four fascicles that surround CN II
o Innervated by CN VI
Clinical note: The recti mm. of the eyes are neurally controlled so that both eyes move in unison. Normally, these
muscles are held in tonic contraction until the animal intentionally moves its eyes to one direction. When the eyes move
laterally, the medial rectus m. is inhibited while the lateral rectus m. is contracted. If one of the rectus muscles is
paralyzed, the eye is pulled in the direction of the unopposed muscle (if the dorsal rectus is paralyzed, the eye will be
pulled ventrally). Displacement of the eyeball from the normal central position is called strabismus.
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Optic n.
 Only cranial nerve covered by dura mater
 Long ciliary nn. of CN V1 course along the optic n. (very difficult to see grossly)
o These nerves provide GSA to the cornea
Oculomotor n.
 Exhibits a “Y” shaped forking point where the ciliary ganglion is located
 Exhibits connections to the optic n. called short ciliary nn.
o These nerves provide postganglionic parasympathetics to the pupillary constrictors
Frontal n.
 Branch of ophthalmic n. of CN V
 Located dorsal to the dorsal rectus m.
Infratrochlear n.
 Branch of ophthalmic n. of CN V
 Located ventral to the dorsal rectus m
Branches of the maxillary a. supply blood to the structures of the eyeball. After its exit from the alar canal (via
the rostral alar foramen), the maxillary a. gives off an external ophthalmic a.
 This artery enters the periorbita and gives off dorsal and ventral muscular branches the supply the
extraocular muscles as well as the lacrimal gland. They are continued rostrally by ciliary aa. that supply
the conjunctiva as well as the deeper structures of the eye (i.e. ciliary body, iris)
INTERNAL EYE
- Fibrous coat
 Cornea (transparent and circular)
 Sclera
o Dense and opaque, dull gray to white colored
o Extra-ocular muscles insert on its wall
o Highly penetrated by blood vessels and nerves (including CN II)
 Limbus (corneoscleral junction)
- Vascular coat (uvea)
 Iris (anterior uvea)
o Pupil (is an opening, not a structure)
 Ciliary body (contains numerous muscle bundles that regulate the shape of the lens)
 Choroid (posterior uvea, firmly attached to the sclera)
 Ora serrata
o Junction of choroid and ciliary body
o Seen as an undulating line on the overlying retina
- Internal (nervous) coat
 Consists of the retina and its associated blood vessels and nerves
 Pars optica retina
o Portion of the retina containing rods and cones (light-sensitive), bipolar, and ganglion cells
o Covers the internal surface of the choroid up to the ora serrata
 Pars ciliaris retina (non-light receptive; passes over the posterior surface of the ciliary body)
 Pars iridica retina (non-light receptive; extends from pars ciliaris retina to posterior surface of the iris)
- Lens (bounded anteriorly by the iris and aqueous humor and posteriorly by the vitreous body)
 Anterior chamber (chamber between the cornea and iris)
o Aqueous humor is drained from this chamber at the iridocorneal angle
 Posterior chamber (chamber between the iris and the lens)
- Fundus
 Posterior, deep portion of the eyeball that is seen with an ophthalmoscope
 Composed of the optic disc, tapetum lucidum, and tapetum nigrum
o Optic disc
 Entrance of the optic n. into the posterior aspect of the eyeball
o Tapetum lucidum (specialized layer of choroid cells that reflects light)
o Tapetum nigrum (non-tapetum lucidum portion on the interior of the eyeball)
EXTERNAL EAR
- The skeleton of the external ear is composed of three elastic cartilages: annular, auricular, and scutiform
 Annular and auricular cartilages form the external acoustic meatus
 Auricular cartilage expands to form the auricle (pinna)
- Apex (tip of the auricle)
- Scapha (central region of the auricle)
- Lateral helix
 Lateral border of the auricule
 Exhibits a cutaneous pouch called the cutaneous marginal pouch
- Medial helix (medial border of the auricle)
- Anthelix (transverse ridge on the internal wall of the auricle marking the caudal boundary of the ear canal)
- Tragus (thick cartilage plate opposite the anthelix marking the rostral boundary of the ear canal)
- Antitragus (cartilagenous projection representing the lateral boundary of the ear canal)
- Intertragic incisure (separates the tragus and antitragus cartilages)
- Pretragic incisure (separates the lateral and medial crura of the helix)
- Scutiform cartilage (over temporalis m.)
 Small cartilage plate located over the temporalis m.
 Acts as a fulcrum by providing muscles that attach to it efficient movement of the auricle
 Does not contribute to the formation of the external ear
NOSE and LIPS
- Muzzle (rostral portions of upper and lower jaw together)
- Nasal plane
 Apex of the nose that is flat, devoid of hair, and often pigmented
 Epidermal pattern is unique in each animal and may be used for “nose printing”
- Nostril (leads into the nasal vestibule and nasal cavity)
- Nasal ala (dorsolateral aspects of the nostrils)
- Nasal sulcus (groove that leads into the nostril)
- Nasal philtrum (separates the nostrils and is continuous with the labial philtrum)
- Lower lip (exhibits denticulate papillae)
- Upper lip (no papillae)
- Labial commissures represent the union of the upper and lower lips
- Buccal (cheek) vestibule
 Bounded laterally by the superior and inferior labia (lips)
 Bounded medially by the teeth and gums
- Labial vestibule (more rostral than the buccal vestibule)
- Sinus hairs are specialized, tactile hairs located at various locations on the face
 Buccal sinus hairs (1-3 on the cheek)
 Supraorbital sinus hairs (4-8 on the medial aspect of the upper eyebrow)
 Zygomatic sinus hairs (1-3 on the zygomatic arch)
 Superior labial sinus hairs (4 rows on the upper lip)
 Inferior labial sinus hairs (2 rows on the lower lip)
 Mental sinus hairs (1-3 on the chin)
 Intermandibular sinus hairs (1-3 between the mandible bones)
- Nasal septum
 The nasal cavity is the bony facial part of the respiratory passages and is composed of two symmetrical
halves separated by a median nasal septum
o Bony part begins at the nasal apertures
o Caudal openings of the nasal cavity are the choanae, which lead into the nasopharynx
ORAL CAVITY
- The oral cavity proper is bounded dorsally by the hard palate, ventrally by the tongue, laterally and rostrally by
the teeth, and caudally by the palatoglossal fold
- Hard palate
 Composed of bone and mucous membrane
 Entire mucous membrane exhibits palatine ridges (6-10 in number)
o Palatine ridges of the cat exhibit cornified papillae
 Median ridge terminates rostrally at the incisive papilla (caudal to upper incisors)
o Papilla represents the embryonic primary palatine process
- Soft palate
 Highly muscular caudal continuation of the hard palate
 Associated with three pairs of skeletal muscles
o Levator veli palatini m.
 Extends from the muscular process of the temporal bone to the soft palate
 Innervated by the pharyngeal n. of CN IX
 Elevated the soft palate
o Tensor veli palatini m.
 Extends from the muscular process of the temporal bone to the soft palate
 Tendon hooks under the hamulus of the pterygoid bone
 Innervated by the nerve of the tensor veli palatini m. of CN V3
 Helps to depress the soft palate
o Pterygopharyngeus m.
 Arises from the pterygoid bone and inserts on the dorsal wall of the pharynx
 Constricts and shortens the pharynx
Clinical note: During early gestation, the nasal and oral cavities are separated by formation of the hard and soft palate. This
occurs through fusion of the primary and secondary palatine processes. Incomplete fusion of the primary palate results in cleft lip
while incomplete fusion of the secondary palatine processes results in cleft palate. Usually the two occur together. This condition
results into food and saliva entering the nasal cavity, resulting in serious conditions that must be repaired surgically.
PERMANENT DENTITION
- Dog
I 3/3 C 1/1 PM 4/4 M 2/3
 Carnassial teeth are upper PM4 and lower M1
- Cat
I 3/3 C 1/1 PM 3/2 M 1/1
 Carnassial teeth are upper PM 4 and lower M3
TONGUE
- Body (rostral 2/3)
- Root (caudal 1/3)
- Dorsal sulcus of the tongue
- Lingual frenulum
 Ventral median fold of mucosa that attaches the rostral tongue to the floor of the oral cavity
- Sublingual caruncle
 Slight raise of mucosa that protrudes from the floor of the oral cavity lateral to the frenulum
 The mandibular and major sublingual salivary ducts open on or beside this structure
- Sublingual fold
 Caudal extension of the caruncle where the mandibular and major sublingual ducts are found
- The mucosa of the tongue is modified to form various types of papillae
 Filiform papillae
o Arranged in diagonal rows on the dorsal surface of the tongue
o Can be soft (dog) or firm and used for grooming (cat)
o No associated taste buds
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Fungiform papillae
o Found only on the dorsal surface on the body of the tongue
o Taste buds are innervated by the chorda tympani n. of CN VII
Vallate papillae
o 2-3 pairs of papillae found at the junction of the body and root of the tongue
o Taste buds are innervated by the lingual n. of CN IX
Foliate papillae
o Found on the lateral edges of the root of the tongue
o Associated with taste buds in the dog (not the cat)
Conical papillae
o Found only on the root of the tongue
o Have pointed tips that serve a mechanical function
Lyssa
 Special cylindrical structure located at the ventral tip of the tongue of carnivores
 Filled with striated muscle, fat, and cartilage in the dog
 Mainly composed of fat in the cat
 May be a supportive element of the tongue, aiding in lapping fluids
Sensory innervation to the tongue
 Body of the tongue is innervated by GSA fibers from CN V
 Body of the tongue is innervated by GSA fibers from the chorda tympani n. of CN VII
 Root of the tongue is innervated by GVA and SVA fibers from CN IX
 Taste buds on the caudal root of the tongue are innervated by SVA fibers from CN X
 Taste buds on the caudal surface of the epiglottis are innervated by SVA fibers from CN X
Clinical note: One characteristic feature of gustatory innervation is the nerve’s tropic influence on the taste bud. Without the SVA
innervation, the taste bud atrophies. If CN IX is damaged, the vallate papillae on the affected side atrophies. Similarly, if the
fungiform papillae are atrophied on the right side of the tongue, a right CN VII problem is suspected.
LINGUAL MUSCLES
- Both the extrinsic and intrinsic muscles of the tongue are innervated by CN XII
 Styloglossus m.
o Arises from the stylohoid bone and inserts on the middle of the tongue
o Retracts and elevates the tongue
 Hyoglossus m.
o Arises from the thyrohoid and basihyoid bones and inserts on the root of the tongue
o Lies medial to the styloglossus m.
o Retracts and depresses the tongue
 Genioglossus m.
o Lies in between the geniogyoideus m. (medially) and the hyoglossus m. (laterally)
o Caudal fibers protrude the tongue
o Rostral fibers retract the apex of the tongue
 Intrinsic tongue mm.
HYOID MUSCLES
- The hyoid muscles are associated with the hyoid apparatus, which suspends the larynx and anchors the tongue
- They function in swallowing, lolling, lapping, and vomiting
- Sternohyoideus m.
 Originates on the sternum and inserts on the basihyoid bone
 Innervated by the ventral branches of cervical spinal nerves and CN XII
- Thyrohyoideus m.
 Lies dorsal to sternohyoideus m.
 Extends from the thyroid cartilage of the larynx to the thyrohyoid bone
 Innervated by the ventral branches of cervical spinal nerves and CN XII
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Geniohyoideus m.
 Deep to the mylohyoideus m.
 Arises on the intermandibular articulation and attaches to the basihyoid bone
 Innervated by CN XII
 Draws the hyoid apparatus and larynx rostrally
Mylohyoideus m.
 Spans the intermandibular space
 Arises as a thin sheet of transverse fibers from the medial surface of the body of the mandible, joins
itself at the midline raphe, and inserts on the basihyoid bone
 Forms a sling that supports the tongue
 Innervated by CN V3
LARYNX
- Epiglottis (epiglottic cartilage)
 Lies at the entrance to the larynx
 Anchors caudal edge of the soft palate under it during nose breathing or over it during oral breathing
 Acts as a door to close off the larynx during swallowing
o This is a passive process aided by the caudal movement of the base of tongue
o Also aided by adduction of arytenoids and contraction of pharyngeal muscles
 Taste buds on the caudal surface of the epiglottis are innervated by SVA fibers from CN X
- Arytenoid cartilage
 Cuneiform process (rostral process)
 Corniculate process (dorsal process)
- Ary-epiglottic fold
 Mucosal fold connecting lateral margin of the epiglottis to cuneiform process of the arytenoid cartilage
- Vestibular fold
 Extends from the ventral thyroid cartilage to the ventral cuneiform process
 Forms the rostral boundary of the lateral ventricle
- Vocal fold
 Extends from the mid-ventral thyroid cartilage to the vocal process of the arytenoid cartilage
 Forms the caudal boundary of the lateral ventricle
- Lateral (laryngeal) ventricle
 Diverticulum of laryngeal mucosa
 Bounded rostrally by the vestibular fold and caudally by the vocal fold
 May function to increase resonance or amplify vocalization
- Cricoarytendoideus dorsalis m.
 Functions to dilate the larynx by adduction of the arytenoid cartilages
 This muscle is the only dilator of the larynx
 Innervated by the recurrent laryngeal n. of CN XI that is given off by CN X
PHARYNX
- Nasopharynx
 Extends from choana to palatogpharyngeal fold
 Exhibits opening to the auditory tube (communication with the tympanic cavity)
- Oropharynx
 From palatoglossal fold to palatopharyngeal fold
 Caudal to the palatoglossal fold, a palatine tonsil is located within the tonsilar fossa and covered by
the semilunar fold
- Laryngopharynx
 From palatopharyngeal fold to pharyngo-esophageal limen
PHARYNGEAL MUSCLES
- The pharyngeal muscles aid in swallowing and are all innervated by the pharyngeal branches of CN IX and X
 Cricopharyngeus m.
o Arises from the lateral surface of the cricoid cartilage
o Inserts on the median dorsal raphe of the laryngopharynx
o Innervated by the pharyngeal n. of CN X
 Thyropharyngeus m.
o Arises from the lateral thyroid cartilage
o Inserts on the median dorsal raphe of the pharynx
o Rostral to the cricopharyngeus m. and caudal to the hyopharyngeus m.
o Innervated by the pharyngeal n. of CN X
 Hyopharygeus m.
o Arises from the lateral surface of the thyrohyoid and ceratohyoid bones
o Passes over the larynx and pharynx to insert on the median dorsal raphe of the pharynx
o Innervated by the pharyngeal n. of CN X
 Stylopharyngeus m.
o Arises from the stylohyoid bone
o Inserts on the dorsolateral wall of the pharynx
o Innervated by the pharyngeal n. of CN IX
o Only dilator of the pharynx
 Palatopharyngeus m.
o Arises from the soft palate and inserts on the lateral and dorsal walls of the pharynx
o Constricts and shortens the pharynx
o Innervated by the pharyngeal n. of CN X
 Pterygopharyngeus m.
o Arises from the pterygoid bone and inserts on the dorsal wall of the pharynx
o Innervated by the pharyngeal n. of CN X
o Constricts and shortens the pharynx
NERVES
- Maxillary n. (CN V2)
 Zygomatic n.
o Courses within the periorbita lateral to the lateral rectus m.
o Divides into 2 branches
 Zygomaticotemporal n. (located more dorsally)
 Zygomaticofacial n.
 Intraorbital n.
o Travels within the infraorbital canal and gives off many branches that innervated the teeth
o Exits the infraorbital foramen to supply nasal mucosa and skin of the nose and upper lip
 Pterygopalatine n. (reflect infraorbital to locate)
o Runs along lateral surface of the medial pterygoid m., ventral to the pterygopalatine ganglion
o Pterygopalatine ganglion
 Nerve of the pterygoid canal
o Minor palatine n.
- Mandibular n. (CN V3)
 Lingual n.
o Branches supply intrafusal fibers of tongue muscles and have a proprioceptive function
o Joins the chorda tympani n. of CN VII (provides taste to the body of the tongue)
 Inferior alveolar n.
o Arises caudal to the lingual n.
o Enters mandibular foramen and passes through mandibular canal, giving off branches to the
lower teeth. Exits the canal via mental foramina as the mental nn., which supply the lower lip
 Myelohyoid n.
o Arises caudal to inferior alveolar n.
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Auriculotemporal n.
o Large branch that leaves the parent CN V3 at the oval foramen
o Gives off sensory branches to the skin of the inner external ear canal and tympanic membrane
o Parotid branches of CN V carry postganglionic parasympathetic fibers from the otic ganglion
of CN IX to supply the parotid salivary gland
Buccal n.
o Courses ventral to the zygomatic salivary gland
o Carries postganglionic parasympathetic to the zygomatic salivary gland
o Supplies GSA fibers to the skin and mucosa of the cheek
Clinical note: Zygomatic salivary gland abscess may affect the buccal n. of CN V. This results in the loss of GSA from cheek
mucosa. Consequently, the animal may not feel when the mucosa is accidentally chewed, resulting in buccal ulceration.
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Abducent n. (CN VI)
 Locate at the origin of the lateral rectus m.
CN VII innervates all of the superficial muscles of the head and face, the caudal belly of the digastricus m., and the
platysma m. The nerve enters the petrosal part of the temporal bone through the internal ear canal, courses
through the facial canal of the bone, and exits the cranial cavity. After CN VII exits the facial canal via the
stylomastoid foramen, it gives off the following identifiable branches
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Auriculopalpebral n.
o Rostral auricular n. innervates the rostral auricular muscles
o Palpebral n. courses over the zygomatic arch to the eye to supply the following muscles
 Orbicularis oculi m., retractor anguli oculi lateralis m., and levator nasolabialis m.
Caudal auricular n.
o Motor nerve to the platysma m. and caudal auricular muscles
Dorsal and ventral buccal nn.
o Course over the lateral surface of the masseter m. giving off numerous communicating
branches
o Terminal branches are distributes to the following muscles
 Zygomaticus m., buccinator m., muscles of the lip and nostril
o Dorsal buccal n. receives sensory communicating branches from auriculotemporal n. of CN V
Cervical n.
o Sometimes given off as a branch from the ventral buccal n.
o Runs over lateral surface of the mandibular salivary gland to innervate the following muscles
 Platysma m, parotidoauricularis m., sphincter colli profundus m.
Clinical note: The vagus n. gives off a communicating branch to CN VII after its exit from the facial canal. Thus, vagal branches
are distributed to the skin of the external acoustic meatus via the lateral internal auricular nn. of CN VII. Extreme irritation of
the external ear canal (i.e. ear mite infestation) may induce an emetic response due to exciting of vagal efferents to the stomach.
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Glossopharyngeal n. (CN IX)
 Lingual n.
 Carotid n. (buffer n.)
 Pharygneal n.
o Innervates the stylopharyngeus m. (only dilator of the pharynx)
Vagus n. (CN X)
 Nodose ganglion (caudal to the cranial cervical ganglion)
o Cranial laryngeal n. branches from CN X at this ganglion to supply the cricothyroideus m.
 Pharyngeal plexus (formed by branches of CN IX, X, and the cranial cervical ganglion)
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Accessory n. (CN XI)
 Insertion on the sternomastoid and cleidomastoid mm.
Hypoglossal n. (CN XII)
 Innervates all lingual muscles
o Genioglossus m., hyoglossus m., styloglossus m., intrinsic mm. of the tongue
o CN XII courses ventral to the hyoglossus m. and dorsal to the lingual a. and v.
 Ansa cervicalis
o Joins CN XII with the first cervical spinal nerve (C1)
BRANCHES OF THE COMMON CAROTID ARTERY
- Cranial thyroid a.
 Large artery that supplies the thyroid and parathyroid glands, pharyngeal mm., laryngeal mm., cervical
trachea and esophagus, and some muscles
- Two terminal branches of the common carotid a.
 Internal carotid a.
o Exhibits the carotid sinus at its origin
 Bulbous enlargement that functions as a baroreceptor
o Enters, exits, and re-enters the carotid canal to reach the cavernous sinus
o Exits the sinus dorsal to attachment of the pituitary gland and branches to form the cerebral
arterial circle that supplies the brain
 External carotid a.
o Occipital a.
 Branches adjacent to the internal carotid a.
 Supplies the meninges and muscles on the caudal aspect of the skull
o Cranial laryngeal a.
 Ventral branch that supplies the laryngeal and pharyngeal mm.
o Lingual a.
 Branches ventrally and courses rostrally to supply the tonsil and tongue
 Is accompanied by CN XII at the level of the tongue
 Can be used to take arterial pulse when animal is under general anesthesia
o Facial a.
 Courses between the digastricus and masseter mm. to supply the lips and nose
 Sublingual a. branch is accompanied by the mylohyoid n. of CN V3
o Caudal auricular a.
 Branches at the base of the ear
 Provides nourishment to the tissues of the external ear
o Terminates by dividing into two branches
 Superficial temporal a.
o Courses dorsally to supply the parotid gland, eyelids, and the masseter,
temporal, and rostral auricular mm. (via the rostral auricular a.)
 Maxillary a.
o Deep terminal branch that is associated with many cranial nerves
o Inferior alveolar a.
 Enters the mandibular foramen with the inferior alveolar n. and
courses through the mandibular canal
 Supplies branches to the roots of the teeth
o External ophthalmic a.
 Arises as the maxillary a. emerges from the alar canal
 Penetrates the periorbita to supply structures within
o Infraorbital a.
 Termination of the maxillary a.
 Courses through the maxillary foramen and through the infraorbital
canal, giving off branches that supply the teeth
 Emerges from the infraorbital foramen to supply nose and upper lip
VEINS
- External jugular v.
 Union of the maxillary v. and linguofacial v.
 Maxillary v.
o Caudal auricular v.
 Drains the lateral margin of the external ear and some muscles of the ear
o Superficial temporal v.
 Located at the ventral base of the ear
 Drains the temporalis m. and most of the external ear
 Receives the rostral auricular v.
 Linguofacial v.
o Union of the facial v. and lingual v.
o Facial v. (related to the mandibular lymph nodes)
 Inferior labial v.
 Deep facial v.
 Superior labial v.
 Angularis oculi v.
o Lingual v.
 Courses between the genioglossus and hyoglossus mm.
 Runs with the lingual a. along the dorsal margin of the hyoglossus m.
 Forms the hyoid venous arch
o Joins the left and right lingual veins
- Internal jugular v.
 Begins at the tympano-occipital fissure
 At its origin, is associated with internal carotid a. and is enclosed by the carotid sheath (only in the dog)
 Drains the thyroid gland
 Terminates when it joins the external jugular v. in the lower neck
SALIVARY GLANDS and associated structures
- Parotid salivary gland
 Predominantly serous gland
 Parotid salivary duct courses on the lateral surface of the masseter m.
o Opens into the buccal vestibule opposite the upper carnassial tooth (PM 4)
 Innervated by GVE fibers from CN IX
 Related to the dorsal and ventral buccal, auricular, and auriculopalpebral branches of CN VII
 Related to the auriculotemporal n. of CN V
Clinical note: Parotid gland infections and tumors may involve the facial n. Surgical removal of the gland requires knowledge
of the location of the facial n. Damage to the auriculopalpebral and buccal branches of CN VII during parotid gland removal
can result in lack of blink reflex, subsequent corneal lesions, and buccal paralysis.
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Mandibular salivary gland
 Mixed gland composed of serous and mucinous acini (predominance of mucinous in dog)
 Within thick CT capsule
o Capsule also encases the caudal part of the monostomatic sublingual salivary gland
 Mandibular salivary duct opens on the sublingual caruncle
 Lateral surface of the gland is crossed by the cervical branch of CN VII
 Innvervated by GVE fibers from CN VII
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Sublingual salivary gland
 Mixed gland with both serous acini and demilunes
 Extends from the rostral border of the mandibular salivary gland to the mandibular ramus
 Innervated by GVE fibers from CN VII
 Monstomatic salivary gland
o Caudal part located within the capsule of the mandibular salivary gland
o Rostral part
o Duct open on the sublingual caruncle
 Polystomatic salivary gland
o Duct opens at the back of the mouth
Clinical note: Ranula is a sublingual salivary mucocele (collection of saliva usually from sublingual salivary glands) that may
result from tears in salivary ducts or salivary gland tissue secondary to trauma or foreign body obstruction. This condition is more
common in the dog than cat and may interfere with prehension, cause bleeding, or create difficulty breathing and swallowing.
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Zygomatic salivary duct
 Located medial and ventral to the zygomatic arch
 Duct opens into buccal vestibule opposite the last upper molar (1cm caudal to parotid duct opening)
 Innervated by GVE fibers from CN IX
Clinical note: If the zygomatic salivary gland must be removed due to pathology, care must be taken to avoid important related
structures. Anatomical relationships to the gland are: (dorsally) globe, (laterally) deep facial v., (ventrally) medial pterygoid m.,
maxillary a., maxillary n. branches, and pterygopalatine ganglion.
LYMPHATICS
- Mandibular lymph nodes
 Located on the either side of the facial v.
- Parotid lymph node
 Located along the rostral margin of the parotid salivary gland
 Innervated by GVE fibers from CN IX
- Medial retropharyngeal lymph node
 Final collecting point for structures of the head
 Dorsal to the common carotid a. at the larynx
MISCELLANEOUS
- Thyroid gland
 Darkly colored and usually consists of two separate lobes
 Loosely attached to trachea and usually lying lateral to the first five tracheal rings
- Parathyroid glands
 Two parathyroid glands associated with each thyroid lobe
o External parathyroid most commonly lies in the fascia of the thyroid gland
o Internal parathyroid lies deep within the thyroid capsule
- Cervical part of esophagus
 Extends from the laryngopharynx to the thoracic portion of the esophagus at the thoracic inlet
- Trachea
 Composed of ~35 tracheal cartilages
o These cartilages are open dorsally, creating a space that is bridged by the trachealis mm.