218 THE ANATOMY OF THE HORSE. 



The 3rd Cranial Nerve, or Motor Oculi, issues from the foramen 

 lacerum orbitale, and supplies the following muscles : — the superior, 

 internal, and inferior recti ; the corresponding fasciculi of the retractor 

 oculi; the inferior oblique; and the levator palpebrse superioris. It 

 also gives the motor root to the ciliary ganglion, and thus supplies the 

 ciliary muscle and the circular fibres of the iris. 



The 4th Cranial Nerve (called also the trochlear or pathetic nerve) 

 issues by the pathetic foramen, and is wholly distributed to the superior 

 oblique muscle. 



The 6th Cranial Nerve, ,or Abducbns, issues by the foramen lacerum 

 orbitale, and is distributed to the external rectus and the subjacent 

 fasciculus of the retractor oculi. 



The Ciliary Ganglion, called also the ophthalmic or lenticular 

 ganglion. This minute ganglion should be sought near the origin of 

 the nerve to the inferior oblique muscle. Find that nerve entering the 

 muscle, and trace it back to its origin from the motor oculi. From its 

 minute size, the ganglion is likely to have been disturbed in the 

 previous dissection ; and in order to display, it satisfactorily a special 

 dissection is necessary. The nerves which pass to and from the 

 ganglion may be arranged as follows : — 



Afferent Branches. — (1) A motor root from the 3rd nerve, (2) a sensory 

 root from the palpebro-nasal nerve, (3) a sympathetic root from the 

 cavernous plexus, joining the ganglion independently or (more commonly) 

 with the sensory root. 



Efferent Branches. — These are the ciliary nerves. They pierce the 

 sclerotic and are distributed to the eyeball, and will be again referred 

 to in the dissection of that organ. 



The optic foramen, through which the optic nerve issues, is one of a 

 group of foramina termed the orbital hiatus, or the orbital group of 

 foramina. When the head is vertical there lies below this, at the 

 posterior and inner part of the orbit, another group of foramina — the 

 maxillary group or hiatus. The internal maxillary artery and the 

 superior maxillary division of the 5th nerve pass iTetween these two 

 groups, and in that course detach several important branches. Their 

 dissection is conveniently undertaken after that of the muscles, vessels, 

 and nerves of the eye. 



The Internal Maxillary Artery issues from the lower orifice of the 

 subsphenoidal or pterygoid canal, and descends to the maxillary hiatus, 

 where it is directly continued as the palato-labial artery. While within 

 the canal it detaches the ophthalmic and anterior deep temporj,! arteries. 

 After its emergence it gives off the buccal, superior dental, staphyline, 

 and spheno-palatine arteries. 



The Ophthalmic Artery issues from the subsphenoidal canal along 

 with the parent artery. It has already been followed. 



