THE HORSE. 



173 



the largest nerves of the brain. They take 

 then- origin by filaments from the crura cere- 

 belli, and pierce the dm*a mater. Each 

 nerve appears to form a ganglion ; from 

 this ganglion we say that three nerves de- 

 part. One is called the ophthalmic; the 

 second, the anterior maxillary ; the third is 

 the posterior maxillary nerve. The oph- 

 thalmic nerve is the smallest of the three 

 divisions ; as it emerges from the orbit, it 

 divides into three branches, called the 

 lachrymal, the super-orbitar, and the lateral 

 nasal branch. 



The second division., or antei'ior maxillary 

 nerve, leaves the cranium through the hole 

 called foramen rotundum, of the sphenoid 

 bone, and takes its passage through the 

 inferior orbital canal, whence it emerges, 

 covered by the levator labii superioris, 

 upon the face : here it splits into several 

 large branches, denominated the facial 

 nerves- But prior to its entering this canal 

 it detaches several important branches to 

 the eyelid, lachrymal duct ; also several 

 long filaments, which descend on the tube- 

 rosity of the anterior maxilla, penetrate the 

 bone, and furnish twigs to the antrum, and 

 the two [superior molar teeth. The largest 

 branch is the spheno-palatine, or lateral 

 nasal nerve, to wiiich the foramen spheno- 

 palatine gives passage into the nose, 

 wherein it divides into two sets of fila- 

 ments. One of these is spread over the 

 lateral parietes of the nasal cavity ; the 

 other ramifies over the sinuses, and sends 

 a filament to the lower border of the sep- 

 tum. A branch also goes to the velum 

 palati, and another branch accompanies the 

 palatine blood-vessels, and ramifies over the 

 soft palate. 



The facial branches of this division ter- 

 minate on the front and sides of the face, 

 and receive communicating filaments from 

 the anterior facial branch of the portio 

 dura, and with them form a plexus. 



The third division, the posterior maxillary 

 nerve, gives off a branch which runs up in 

 front of the parotid gland, and joins the 

 portio dm-a; also branches called the buc- 

 cal nerve, pterygoideus, and gustatory. The 



latter descends by the side of the tongue, 

 penetrates that organ about its middle, and 

 vanishes in its tip. It also sends ramifica- 

 tions to the roots of the incisive teeth, and 

 to the under lip. 



Sixth pair, or abducentes, arise by means 

 of filaments from the medulla oblongata ; 

 this nerve gives off two or three filaments 

 to the retractor oculi; but its principal des- 

 tination is to the abductor, along the fasci- 

 cula of which, its ramifications are equally 

 distributed. 



Seventh jjair, or auditory nerves. — This 

 pair includes two separate nerves on either 

 side ; one, from its remarkable softness, is 

 denominated the portio mollis ; the other, 

 in contradistinction, the portio dura. The 

 portio mollis enters the organs of hearing, 

 and is distributed to the labyrinth. 



The portio dura arises from the medulla 

 oblongata, and passes to the internal part 

 of the ear, the tympanum, and eustachian 

 tube. It is also distributed to the temples, 

 eyelids, nose, lips, cheek, and neck. 



Eighth pair, or par vagum. — At its 

 commencement it consists of two separate 

 portions ; the first called the glosso-pharyn- 

 geal nerve, and the second the true par va- 

 gum. They arise from the corpora ohvaria, 

 and make their exit through the base of the 

 cranium. The glosso-pharyngeus gives off 

 branches, which join the portio dura, to the 

 constrictors of the pharynx, and form 

 branches which ramify in the base of the 

 tongue. 



The proper par vagum, having disunited 

 from the glosso-pharyngeal nerve, proceeds 

 downwards to join the carotid artery, and 

 takes its course along the neck to the chest. 

 Its filaments are — 1. To the cervical gan- 

 glion. 2. The pharyngeal branch, whose 

 filaments pass to the esophagus and larynx. 

 3. Two slender branches to the carotid ar- 

 tery, which form a plexus. 4. The laryngeal 

 branch. 



At the back part of the neck the par 

 vagum inclines upwards, and is found 

 above the carotid artery ; it then passes 

 between the two first ribs into the chest. 

 Having entered the thoracic cavity, it runs 



