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 palpebrae 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 Abducens, 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 to be 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 between 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 temporal 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. 



