MAMMALIA. 129 



continuation from the thalamus, after this has received the true visual tract ; it is 

 connected with the surface of the nates, the geniculate body, the sensitive tract, 

 the mammillary eminence and the part surrounding this ; the commissure is not 

 generally so large as in man, therefore each nerve passes more directly to its foramen, 

 and is longer or shorter in different animals according to the nearer or more distant 

 position of the eye with respect to the brain ; it becomes expanded into a soft retina, 

 similar to that in man. 



In mammalia, the third nerve arises from the inner side of the crus of the brain, 

 as in man ; it passes into the orbit and supplies all the muscles except the superior 

 oblique, the abducent and retractor. It sends a branch to be joined by one from the 

 fifth in the ciliary ganglion ; from which, in the monkey, branches similar to those in 

 man proceed to the interior of the eye ; in the porpoise the ganglion is joined by a 

 branch from the third and fifth ; but in many other animals the ganglion is by no 

 means proportionate to the size of this organ, and sends off only a few thick branches ; 

 more branches of the fifth, however, appear to terminate on the eye-lids and the 

 conjunctive membrane. In the jaguar, there is a ganglion on the portion of the third, 

 which eventually terminates in the inferior oblique muscle ; it sends a branch to pass 







on the outer side of the optic nerve into the eye ; it sends also a very large branch to 

 be joined by a branch from the superior nasal, but not to form a ganglion, and from 

 this junction branches pass along the inner side of the optic nerve into the eye ; the 

 ciliary ganglion and nerves are larger in proportion to those of the ass and sheep, 

 but the branches entering the eye are not so numerous as in man. In the pig, the 

 third nerve supplies the usual muscles of the eye, and gives off some ciliary filaments. 

 A branch of the third is then joined by a nerve formed of two branches ; one pro- 

 ceeding from the first trunk of the fifth, the other from the beginning of the second 

 trunk, at a spot at which a branch of the sympathetic is received. After this union, 

 it gives off ciliary filaments to pass along the optic nerve ; it is then directed to 

 terminate in the inferior oblique muscle. The ciliary nerves are very insignificant, 

 but numerous branches of the fifth supply the eyelids. In the calf, the branch of the 

 fifth, joining the branch of the third in the ciliary ganglion, arises from the Gasserian 



s 



