796 NERVOUS SYSTEM OF THE HORSE 



the levator palpebrse superioris and ramifies chiefly in the lacrimal gland and the 

 upper eyelid. A branch (Ramus zygomatico-temporalis) exchanges twigs with the 

 zygomatic branch of the maxillary nerve, perforates the periorbita, and emerges 

 from the orbital fossa behind the supraorbital process; it forms a plexus with 

 branches of the auriculo-palpebral and frontal nerves, and ramifies in the skin of 

 the temporal region. 



2. The frontal nerve (N. frontalis), also termed the supraorbital, runs forward 

 almost parallel with the dorsal oblique muscle, at first within, then outside of, the 

 periorbita. It passes through the supraorbital foramen with the artery of like 

 name and ramifies in the skin of the forehead and upper eyelid, forming a plexus 

 with the lacrimal and auriculo-palpebral nerves. It divides into three branches. 



3. The naso-ciliary nerve (N. nasociliaris), also termed the palpebro-nasal, 

 runs forward along the medial side of the optic nerve between parts of the retractor 

 muscle and divides into two branches. Of these, the ethmoidal nerve (N. ethmoid- 

 ahs) is the continuation of the parent trunk. It accompanies the ethmoidal 

 artery through the foramen of like name into the cranial cavity and crosses the 

 lower part of the ethrhoidal fossa. Leaving the cranium through an opening in the 

 cribi-iform plate close to the crista galli, it enters the nasal cavity and ramifies in 

 the mucous membrane of the septum nasi and the dorsal turbinate. The infra- 

 trochlear nerve (N. infratrochlearis) runs forward to the medial canthus and rami- 

 fies in the skin in this region; it detaches twigs to the conjunctiva and caruncula 

 lacrimalis, and a long branch which supplies the third eyelid and the lacrimal ducts 

 and sac. The naso-ciliary nerve furnishes the sensory or long root (Radix longa) 

 of the ciliary ganglion. 



The ciliary ganglion is placed on the ventral branch of the oculomotor nerve, 

 close to its origin /rom the latter. It is usually not larger than a millet-seed, and 

 is best found by following the nerve to the ventral oblique muscle back to its origin. 

 The ganglion receives — (a) sensory fibers from the naso-ciliary nerve; (6) motor 

 fibers from the oculomotor nerve; and (c) sympathetic fibers from the spheno- 

 palatine plexus. It detaches filaments which unite with twigs from the ophthalmic 

 and maxillary nerves and from the sphenopalatine ganglion to form the ciliary 

 plexus. From the latter emanate five to eight delicate short ciliary nerves (Nn. 

 ciliares breves), which pursue a somewhat flexuous course along the optic nerve, 

 pierce the sclera near the entrance of that nerve, and run forward between the 

 sclera and chorioidea to the circumference of the iris. Here the branches of ad- 

 jacent nerves anastomose to form a circular plexus (Plexus gangliosus ciliaris), 

 from which filaments go to the ciliary body, iris, and cornea. 



The circular fibers of the iris and the ciUary muscle are innervated by fibers derived from the 

 oculomotor nerve, the radial fibers of the iris by the sympathetic. 



II. The maxillary nerve (N. maxillaris)^ is purely sensory and is much larger 

 than the ophthalmic. It extends forward from the semilunar ganglion in the middle 

 cranial fossa in the large groove on the root of the temporal wing of the sphenoid. 

 It is related medially to the cavernous sinus and dorsally to the ophthalmic nerve, 

 with which it is blended for some distance. It emerges through the foramen 

 rotundum, passes forward in the pterygo-palatine fossa above the internal maxillary 

 artery and embedded in fat, and is continued in the infraorbital canal as the in- 

 fraorbital nerve (Fig. 564). Its branches are as follows: 



1. The zygomatic nerve (N. zygomaticus s. subcutaneus malse), also termed 

 the orbital branch, arises before the maxillary nerve reaches the pterygo-palatine 

 fossa (Figs. 563, 564, 646). It pierces the periorbita and divides into two or three 

 delicate branches which pass along the surface of the lateral straight muscle to 



1 This is also termed the superior maxillary branch. 



