Budras_Анатомия лошади

(Median section, the nasal septum has been removed)

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18 Body of tongue

17 Proper oral cavity

16 Apex of tongue

15 Palatine ridges

14 Oral vestibule

20 Nasal diverticulum

(Lateral views)

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8. Pharynx, Guttural Pouch and Larynx

These structures need to be studied from both medial and lateral aspects. The guttural pouch is best opened and explored on a median section of the head. This shows its interior and certain vessels and nerves on its surface to best advantage. To examine position and extent of the guttural pouch and of the pharyngeal constrictors, the pterygoids, digastricus, stylohyoideus, occipitomandibularis, and occipitohyoideus are partly, and the mandibular and parotid glands are completely removed.

1a) The PHARYNX, following the common plan, comprises an oropharynx, a laryngopharynx, and a nasopharynx. The oropharynx

(B) continues the oral cavity at the level of the glossopalatine arch and extends to the base of the epiglottis. The laryngopharynx (C) continues the oropharynx around the rostral parts of the larynx to be continued itself by the esophagus. It is open dorsally via the

2intrapharyngeal opening to the nasopharynx (A). During normal breathing the intrapharyngeal opening allows the rostral parts of the larynx to protrude into the nasopharynx.

The nasopharynx is dorsal to the soft palate where it continues the ventral nasal meatus through the choanae. It communicates via the

3pharyngeal openings of the auditory tubes (2), the auditory tube itself, and the guttural pouch (see further on) with the middle ear.

4The soft palate (3) is about 12 cm long and during normal breathing extends with its free border to the base of the epiglottis. This circumstance makes it very difficult for horses to breathe through their mouth or to vomit. For the same reason vomitus is expelled through the nose. (The reason why vomiting is so rare in horses is related principally to the structure of the stomach; p. 68.)

I. The pharyngeal muscles, their innervation and that of the pharyngeal mucosa by the pharyngeal branches of cranial nerves IX and X follow the common pattern (see also p. 51). The muscles of the soft palate are tensor veli palatini (7) and levator veli palatini

(8). The rostral pharyngeal constrictors, which arise on the skull, are pterygopharyngeus (9) and palatopharyngeus (11). The middle pharyngeal constrictor (from the thyrohyoid) is the hyopharyngeus (12). And the caudal pharyngeal constrictors, which arise from the larynx, are thyropharyngeus (13) and the cricopharyngeus (14).

The only dilator of the pharynx is the stylopharyngeus caudalis (10).

II. The tonsils concentrated in the pharynx include palatine, pharyngeal, lingual, tubal, and those residing in the soft palate. The palatine tonsil (5) is an elongated slightly raised structure, about 10 cm long and 2 cm wide, on the floor of the oropharynx lateral to the median glossoepiglottic fold. The pharyngeal tonsil (1) is in the dorsolateral wall of the nasopharynx near the pharyngeal opening of the auditory tube. The lingual tonsil (6) is spread over the root of the tongue, and the tonsil of the soft palate (4) is a slightly raised area rostrally on the ventral surface of the soft palate. The tubal tonsil, not a discrete organ, is diffuse lymphoid tissue in and around the pharyngeal opening of the auditory tube.

III. The auditory tube opens into the lateral wall of the nasopharynx

(A) opposite the lateral angle of the eye. The opening is covered medially by the most rostral part of the tubal cartilage (15), a flap that is drawn medially by the tensor and levator veli palatini during swallowing. The opening leads into the auditory tube supported by the rest of the tubal cartilage (shaped like an inverted trough) and into the guttural pouch, which is a great expansion of the unsupported ventral wall of the tube. The caudal end of the auditory tube is in addition supported by bone and opens into the tympanic cavity forming the middle ear.

5b) The GUTTURAL POUCH is a paired airfilled space with a capacity of 300 to 500 ml. It extends from the base of the skull and the atlas to the nasopharynx. The two pouches touch each other ventral to

forms relations with the maxillary vessels (20), the external carotid artery (21) and the facial nerve (VII).

Guttural Pouch

(View of the dorsal wall)

The LARYNX is ventral at the head-neck junction, anchored in position by the hyoid bone (thyrohyoideum). It fulfills the functions of closing the airway and of enabling the animal to form its voice. In swallowing, the entrance to the larynx is safeguarded by retroflex-

2ion of the epiglottis (epiglottis —3). In coughing, to clear the lower airway (see the text-figure), the glottic cleft is first closed and, utilizing the abdominal press, suddenly opened to allow the thrust of air to expel exudate, particulate, and other material. In the operation of the abdominal press, the glottic cleft is closed, in which case the inspiratory position of the diaphragm in the thoracic cavity serves as an opposing pressure-clushion to the increase in pressure in the abdominal cavity. The formation of sound by the larynx is associated with the vocal folds (plicae vocales —V), which surround the glottic cleft and are underlain by the vocal muscle (m. vocalis —11). Owing to the intensity of the air-stream, the vocal folds vibrate and in this way the tone (pitch) of the voice arises. The more that the vocal folds are stretched, the higher is the pitch.

3The equine larynx (see text figures) is characterized by possessing

4; 5 laryngeal ventricles laterally (III, see page 49.10) and a single median recess (IV); otherwise, it follows the common mammalian plan.

The following features of its interior and its cartilages are shown in the two figures on this page and the two figures on page 49: laryngeal vestibule (II), vestibular fold containing the vestibular ligament (II'') and the ventricularis muscle (9), the glottis (see page 47.F) and the glottic cleft (V), which is the space between right and left components of the glottis. See the vocal fold (page 47.F) which contains the vocal ligament (V') and the vocalis muscle (11), and the infraglottic cavity (page 47.G).

6The epiglottic cartilage (3) has right and left cuneiform processes (3'), which project dorsally from its base; the arytenoid cartilage (1) presents corniculate (1'') and vocal (1''') processes and, on its lateral surface, a muscular process. The thyroid cartilage (4) is deeply notched ventrally, creating the thyroid notch. The notch is open caudally and bridged by the cricothyroid ligament. The lamina of the cricoid cartilage (2) overhangs the first tracheal cartilage.

The JOINTS OF THE LARYNX are the cricothyroid (4'''), hinge-like movements that tilt the thyroid cartilage and, in that way, vary the tension on the vocal folds), cricoarytenoid (4'''', for craniocaudal gliding movements) as well as the hyrohyoid articulation (4'', the connection to the hyoid bone).

Of the LARYNGEAL MUSCLES the cricoarytenoideus dorsalis (7), the only dilator of the glottis, is important in “roaring.” The sphincters of the glottis-cricothyroideus (12), cricoarytenoideus lateralis (6), vocalis (11), ventricularis (9), and the arytenoideus transversus (5)

– as well as the innervation of the larynx by the cranial and recurrent laryngeal nerves follow the common mammalian pattern. Occasionally, one finds an accessory thyroarytenoideus that ex-

Clinical and Functional Anatomy p. 161–162

Ventral half of Larynx

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Cricothyroid ligament

tends from the muscular process of the arytenoid cartilage to the dorsal border of the thyroid cartilage, or a tensor of the laryngeal ventricle that begins on the cuneiform process of the epiglottis and fans out to end on the laryngeal ventricle.

INNERVATION. The laryngeal muscles are innervated by the cranial and caudal laryngeal nerves, both branches of the vagus, of which the former is dispatched at the head-neck junction and the latter in the thorax. The cranial laryngeal nerve enters the larynx by the thyroid foramen but before doing so detaches an external branch (b) to the cricothyroideus. The caudal laryngeal nerve (8) is the continuation of the recurrent laryngeal nerve after that nerve’s tracheal and esophageal branches have been given off in its ascent of the neck.

The caudal laryngeal nerve is distributed to the remaining laryngeal muscles. The two nerves also innervate the laryngeal mucosa: the cranial nerve by its internal branch (afferent limb of the cough reflex), which supplies the area up to the glottic cleft. The caudal nerve supplies the area caudal to the glottic cleft.

Larynx

ATympanohyoid cartilage

BStylohyoid bone

CEpihyoid bone

DCeratohyoid bone

EBasihyoid bone

E' Lingual process

FThyrohyoid bone

GThyroid gland

HParathyroid gland

Cranial laryngeal nerve

aInternal branch

bExternal branch

cCommon carotid a.

dCaudal thyroid a.

eCranial thyroid a.

fLaryngeal branch

gAscending pharyngeal a.

hCranial laryngeal a.

iCeratohyoid m.

jTransverse hyoid m.

10. Head-Neck Junction and Ear

The cranial nerves IX through XII and the deeper arteries of the head may be demonstrated both from the side (lateral approach) and, on a split head, from the medial surface. In the former, and in continuation of the dissection, rests of the parotid gland and the guttural pouch (except its median septum) are removed, and so is the proximal (dorsal) third of the stylohyoid and the occipitohyoideus muscle attaching to it. In the more advantageous medial approach the rectus capitis ventralis and longus capitis are taken out so as to demonstrate the neurovascular structures associated with the guttural pouch (see p. 46 and 47).

1a) The EAR can be subdivided into the external ear (auris externa), middle ear (auris media) and internal ear (auris interna). See the text-figures.

The EXTERNAL EAR consists of the auricle with the auricular muscles and scutiform cartilage (scutulum, see page 37) as well as the external acoustic meatus with its cartilaginous part (cartilago auriculae et cartilago anularis; see page 37, D and E) and an osseous part.

The external acoustic meatus (meatus acusticus externus —a) ends at the tympanic membrane (b), the cutaneomembranous border between the external and middle ear. The tympanic membrane consists externally of a cutaneous layer, which is aglandular, hairless, and lacks pigment. It is followed by a middle connective tissue layer. On its side toward the middle ear, the tympanic membrane is clothed with a simple squamous epithelium.

The MIDDLE EAR consists of the pars tympanica of the petrous bone with the tympanic bulla and the auditory ossicles, nerves and muscles contained within it. In the horse, radially arranged bony lamellae form characteristic cellulae tympanicae (d) around the anulus tympanicus (c). The auditory ossicles transmit the sound waves striking the tympanic membrane mechanically to the internal ear. The handle of the hammer (malleus, e) is directly fused with the tympanic membrane. Its head articulates with the body of the incus

(f). With its long crus, the incus transmits the sound waves further to the stapes (g), whose two crura connect via the footplate with the vestibular window of the internal ear. The footplate is joined to the margin of the window by the anular ligament. By way of the tensor tympani muscle (h), the tympanic membrane can be tensed and pulled toward the interior of the tympanic cavity. The stapedius muscle (i) alters the position of the incus and by that favors the transfer of the higher frequencies. On the other hand at normal tonus the stapedius muscle, precisely as does the tensor tympani muscle, prevents damage to the auditory system due to nonphysio-

Middle ear and internal ear*

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Clinical and Functional Anatomy p. 162–163

logical sound effects (intense noise). On the connection of the middle ear with the pharynx by the auditory tube with the expansion of the guttural pouch, see page 46.

The INTERNAL EAR lies totally in the petrous part of the temporal bone. It consists of a system of osseous and membranous canals and is subdivided into the auditory organ with the cochlear duct (duc-

tus cochlearis, j) and the vestibular apparatus (apparatus vestibu- 2 laris, k) or organ of equilibration with the vestibule and the three semicircular ducts that stand perpendicular to one another. Both organs are supplied by the sensory vestibulocochlear nerve (VIII).

b) The deep ARTERIES OF THE HEAD begin with the common carotid (21) which, together with the vagosympathetic trunk, ascends the neck dorsolateral to the trachea. Opposite the second cervical vertebra the common carotid gives off the cranial thyroid artery (18) which sends the ascending pharyngeal artery (g) to the pharynx and, as cranial laryngeal artery (h), curves around the cranial pole of the thyroid gland. Slightly more cranially, the common carotid splits into internal (13) and external (1) carotid arteries. The latter, as it turns dorsally, releases a masseteric branch (2) and the linguofacial trunk (7) which, medial to the mandible, bifurcates to form

lingual (8) and facial (9) arteries. The last-named vessel and its 3 satellite vein are joined by the parotid duct and together they obliquely cross the ventral border of the mandible to gain the face.

The pulse may be taken here on the artery by pressing it against the medial surface of the mandible. (See p. 36 for the veins of the head.)

c)The convex THYROID GLAND (20) is palpable and lies with its right and left lobes dorsolaterally on the trachea immediately caudal to larynx. The lobes are occasionally united ventral to the trachea by a connective tissue isthmus.

d)The PARATHYROID GLANDS are only a few mm in diameter; the external ones lie on the trachea but at a considerable distance from the thyroid glands, about 10 cm cranial to the thoracic inlet. The internal parathyroid glands (19) are either in contact with their respective thyroid lobe or lie within a 1 cm range from it.

e)The ESOPHAGUS continues the pharynx dorsal to the larynx; opposite the fourth cervical vertebra it slips to the left lateral surface of the trachea, and shortly before the thoracic inlet may even gain its ventral surface. It may be divided for description into cervical, thoracic, and (a short) abdominal parts.

f)The TRACHEA continues the infraglottic cavity of the larynx at the cricoid cartilage; its initial portion is covered ventrally by the omohyoideus. It consists of cervical and thoracic parts.

g)The CRANIAL NERVES IX–XI leave the cranial cavity by the jugular foramen and conform to the general pattern.

I. The glossopharyngeal nerve (3), among others releases a lingual branch (5) to the tongue and a pharyngeal branch (4) to the pharynx.

II. The vagus (16) also releases a pharyngeal branch and, in addition, the cranial laryngeal nerve (6) to the thyroid foramen through which it enters the larynx. Before doing so it sends a branch to the cricothyroideus. The vagus passes down the neck within the vagosympathetic trunk and in the thorax it gives off the recurrent laryngeal nerve (22). This reascends to the area of the larynx ventral to the common carotid artery on the dorsalateral aspect of the trachea and enters the larynx by passing deep to thyroid lamina. It innervates all laryngeal muscles (except the cricothyroideus) and the mucosa caudal to the glottis.

III. The accessory nerve (15) splits opposite the atlas into dorsal (r) and ventral (q) branches which innervate trapezius and sternocephalicus, respectively.

h)The HYPOGLOSSAL NERVE (14) enters the region under discussion through the hypoglossal canal and pursues a rostroventral course.

It crosses the medial aspect of the accessory nerve and the lateral aspects of vagus and external carotid artery on its way to supply the intrinsic and the following extrinsic tongue muscles: styloglossus (10), hyoglossus (11), and genioglossus (see p. 45.d). The geniohyoide (see p. 45.j) and thyrohyoideus (12), of the group of hyoid muscles, receive their innervation from the first cervical nerve (C1) which forms the ansa cervicalis (f) with the hypoglossal nerve.

i)The dissection also exposes parts of the AUTONOMIC NERVOUS

SYSTEM such as the sympathetic trunk (17) and the cranial cervical ganglion (17).

Arteries and Cranial Nerves IX, X, XI, and XII of the Head

aInternal carotid nerve of sympathetic trunk

bRectus capitis ventralis

cBranch of glossopharyngeal nerve to carotid sinus

dPharyngeal branch of vagus

eEsophagus

fAnsa cervicalis (C1)

gAscending pharyngeal artery

h Cranial laryngeal artery

iCranial deep cervical lymph nodes

jTrachea

kSternothyroideus

lObliquus capitis cranialis

mSemispinalis capitis

nObliquus capitis caudalis

oLongissimus capitis

pOccipital artery

qVentral branch of accessory nerve

rDorsal branch of accessory nerve

sLongus capitis

tVagosympathetic trunk

uSternohyoideus

13 Internal carotid artery

14 Hypoglossal nerve (N XII)

15 Accessory nerve (N XI)

16 Vagus (NX)

17 Sympathetic trunk and cranial cervical ganglion

Cranial thyroid artery Internal parathyroid gland Thyroid gland

Common carotid artery Recurrent laryngeal nerve

a Nasal septum

a' Membranous part a'' Cartilaginous part a''' Osseous part

bTensor veli palatini

cLevator veli palatini

dPterygopharyngeus

ePalatopharyngeus

fGuttural pouch

gNeurovascular fold associated with the guttural pouch

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2. The Spinal Cord

The spinal cord is best demonstrated from the dorsal aspect, in situ. The arches of the vertebrae and portions of the meninges are removed as shown on the opposite page. (The lower case n preceding the segmental designations stands for nerve.) For the study of the cord’s gray and white substances, central canal, and commissures the cord needs to be transected. Few species-specific features other than size that distinguish the equine spinal cord from those of other domestic mammals. The dissections on the opposite page are from a young, few-months-old horse in which the shortening of the cord (ascencus medullae) in relation to the vertebral canal was still going on. This is why the extents given above for the adult animal do not agree with those in the Figures.

The SPINAL CORD is surrounded and protected by the meninges and with them it occupies the vertebral canal. The end of the cord

(conus medullaris; 20) in the adult horse extends relatively far caudally, to the first sacral vertebra; the filum terminale (21), which prolongs the cord, reaches the fourth sacral segment. Both conus and filum, together with the spinal nerves that flank them for various distances, form the cauda equina (C)which in adult horses begins at the lumbosacral junction.

The central canal on transverse section is a nearly dorsoventrally flattened oval; in the sacral segment, however, it is slightly flattened from side to side. At its caudal end the canal is slightly expanded (ventriculus terminalis; 19) and communicates dorsally with the subarachnoid space. (There is a possibility that both the ventriculus and its communication are artificial post mortem changes.) The number of spinal nerves equals that of the thoracic, lumbar, and sacral vertebrae. In the cervical segment are 8 nerves as in the other domestic mammals, and there are normally only 5 caudal spinal nerves for the innervation of the tail.

Clinical and Functional Anatomy p. 164

Transverse Sections of the Spinal Cord*

Transverse Section at C6

Transverse Section T4