796 NERVOUS SYSTEM OF THE HORSE 
the levator palpebre 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- 
alis) 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 ethmoidal fossa. Leaving the cranium through an opening in the 
eribriform plate close to the erista gall, 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 from 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; (b) 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 ciliary muscle are innervated by fibers derived from the 
oculomotor nerve, the radial fibers of the iris by the sympathetic. 
Il. 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 mm 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 male), 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. 
