HEAD AND NECK OF THE HORSE 113 



superior rectus muscle and the retractor. Its main continuation is the 

 ethmoidal nerve (n. ethmoidalis), which, making a sharp backward 

 bend, enters the cranium by the ethmoidal foramen and thus leaves the 

 present dissection. The collateral branches of the naso-ciliary are the 

 infratrochlear nerve and the long root to the ciliary ganglion. The 

 infratrochlear nerve (n. infratrochlearis) runs forwards along the 

 border of the superior oblique muscle as far as the trochlea, and then 

 follows the medial wall of the orbit to the medial canthus of the eye, 

 where it ends in the skin of this region. Small filaments are furnished 

 to the third eyelid, the lachrymal ducts and sac, the conjunctiva and 

 the lachrymal caruncle. 



N. OCULOMOTORius. — The oculomotor or third cerebral nerve enters 

 the orbit along with the ophthalmic and abducens nerves, and divides 

 into two main branches. The superior branch (ramus superior) supplies 

 twigs to the levator of the upper eyelid and the superior rectus muscle 

 of the eyeball. The larger inferior branch (ramus inferior) supplies the 

 medial and inferior rectus muscles, and its terminal branch enters the 

 inferior oblique muscle after crossing the surface of the inferior rectus 

 obliquely. In addition motor fibres are furnished to the ciliary 

 ganglion. 



The small ciliary ^ ganglion (ganglion ciliare) lies on the inferior 

 branch of the oculomotor nerve close to its point of origin from the 

 parent trunk. The ganglion may be easily overlooked, and is most 

 readily found by tracing the nerve of the inferior oblique muscle to its 

 origin from the oculomotor. Small though the ganglion is, it is of great 

 importance because of the circumstance that through it fibres from the 

 oculomotor nerve reach the circular muscle of the iris and the ciliary 

 muscle, and sympathetic fibres gain the dilator muscle of the pupil. 

 The ganglion receives motor fibres from the oculomotor, sensory fibres 

 (long root) from the naso-ciliary, and sympathetic fibres from the spheno- 

 palatine plexus. From it thin filaments proceed to the ciliary plexus, 

 in the formation of which twigs from the ophthalmic and maxillary 

 nerves and the spheno-palatine ganglion are also concerned. From the 

 ciliary plexus a variable number (6 to 8) of small nerves (nn, ciliares 

 breves) follow the optic nerve, pierce the sclera and run between this 

 coat of the eye and the choroid to end in a plexus at the circumference 

 of the iris. It is from this plexus that fine filaments pass to the iris, 

 ciliary body and the cornea. 



N. ABDUCENS. — The abducent or sixth cerebral nerve enters the 



^ Cilium [L.], an eyelid, an eyelash. The adjective is applied to several 

 structures connected with the eye. 



