644 MR FRANK J. COLE ON THE 



runs upwards and outwards in the vertical fissure separating the ventral portion of the 

 cerebellum from the optic lobe. On emerging from this fissure it courses upwards and 

 forwards, and eventually reaches the orbit under cover of the superficial ophthalmic of 

 the Vllth. It is obscured by the latter for the greater part of its course, but finally 

 takes a dorsal curve, and, appearing above the superficial ophthalmic, is seen to become 

 embedded in the superior oblique muscle of the eye. 



The Abducens, or sixth cranial nerve, arises by six rootlets, one of which is con- 

 spicuous by its size, from the ventral pyramids of the medulla, at a level slightly behind 

 the dorsal root of the Vllth and a little in front of the root of the glossopharyngeal. 

 These rootlets may be traced almost on to the mid-ventral line, and the nerve itself 

 courses in the cranial cavity forwards and slightly downwards, and passes under the 

 roots of the Vth and Vllth, being closely applied to the roots of the Vth. It eventually 

 emerges into the orbit by a foramen hidden by the Vth and Vllth trunks, and slightly 

 anterior to that giving exit to these latter nerves. Once in the orbit, it passes 

 immediately into the external rectus muscle, which it supplies. 



F. The Trigeminus, or Fifth Cranial Nerve. 



Roots. — This nerve, which in Chimasra is in a very primitive condition, being quite 

 distinct from the facial, arises by two closely applied roots from the side of the medulla, 

 under cover and completely obscured by the roots of the buccal division of the facial. 

 These roots are shown separately in fig. 3, the position only of the roots of the Vth being 

 indicated in fig. 1. The roots of the trigeminus have, of course, no connection with the 

 so-called trigeminal lobe. The anterior root is smaller than the posterior ; and although 

 the profundus arises from the anterior margin of the main trunk of the trigeminus, yet 

 it could not be separated from it, and the anterior root cannot, therefore, on anatomical 

 grounds, be considered the root of the profundus in Chimasra. The root thus formed 

 passes through the same foramen in the skull that gives exit to the buccal division of the 

 facial. The latter lies over and obscures the root of the fifth, and it is only after the 

 nerves have emerged into the orbit that the Vth can be seen, when it may be dis- 

 tinguished by its anterior border lying in front of the buccal. Immediately after 

 entering the orbit the trigeminus expands into the large Gasserian ganglion. 



Roots of Vth and buccal. — The main trunk of the Vth, as before stated, enters the 

 orbit accompanied by the buccal division of the facial. Two bundles, as figured by 

 Stannius, may then be distinguished — an anterior and a posterior, but soon afterwards 

 the anterior comes to lie under the posterior. The anterior bundle is the main trunk 

 of the trigeminus, whilst the posterior is almost entirely made up of the buccal nerve. 

 There is this complication : a fairly large bundle leaves the Vth and accompanies the 

 Vllth. This bundle divides into two — a smaller and a larger. The smaller accom- 

 panies the inner buccal (one of the divisions of the buccal) and could not be traced. 



