532 Prof. J. C. Ewart. 



of the higher vertebrates ? These and other questions I shall hope 

 to deal with in a future paper. 



8. The Trochlearis Nerve. : This nerve (8, fig. 1) arises from the side 

 of the brain immediately behind the optic lobe. It passes forward and 

 upwards to pierce the cranium a considerable distance in front of the 

 oculo-motor, it then dips downwards and outwards under the ophthal- 

 niicus superficial to supply the superior oblique muscle. I have 

 been unable to find any sensory branch passing from this nerve in 

 Lcemargus, and in no part of its length does it contain ganglionic 

 cells. 



9. The Abducens. This nerve (9, fig. 1) has a striking resemblance 

 to the anterior spinal nerves. It arises by three or four extremely 

 slender rootlets which are in a line with the rootlets of the oculo- 

 motor in front and the spinal nerves (ventral roots) behind. The 

 rootlets unite to form a trunk which at first lies midway between the 

 auditory and glossopharyngeal nerves. The trunk proceeds forward 

 and perforates the cranial wall to reach and supply the external rectus 

 muscle. The abducens nerve, like the oculo-motor and trochlearis, is 

 devoid of ganglionic cells. It cannot be said to be specially related to 

 the facial complex to form as has been suggested its motor root. 



10. The Auditor)/ Nerve. The auditory nerve (10, fig. 1) lies imme- 

 diately behind and slightly ventral to the common root of the ventral 

 portion of the facial complex. It runs outwards behind these nerves 

 and enters the same cranial canal and at once divides into branches 

 for the auditory apparatus. Although there is no distinct swelling, 

 the root, some distance from its origin, is crowded with ganglionic 

 cells. 



11. The Glossopharyngeal Nerve. This nerve (11, fig. 1) has been 

 long considered one of the most primitive and typical of the cranial 

 nerves. It arises from the side of the medulla in front of and in a line 

 with the rootlets of the middle portion of the vagus, but under cover 

 of the anterior portion of the vagus. The number of rootlets varies, 

 but there is usually one large rootlet and two or three slender ones, and 

 it receives a twig from one of the rootlets of the anterior portion of 

 the vagus. The rootlets together form a small rounded nerve, which 

 passes backwards and outwards through a special canal under the 

 auditory capsule to reach and give two large branches (pre- and post- 

 branchial) to the walls of the first true branchial cleft and a small 

 branch (pharyngeal) to the pharynx. When midway through the 

 walls of the cranium it presents a distinct swelling which is crowded 

 with ganglionic cells. Immediately beyond the ganglion a small 

 dorsal branch takes its origin, which passes upwards through the 

 cranium to reach the skin over the auditory region. Apparently this 

 dorsal branch does not assist in supplying either mucous canals or 

 sensory tubes. 



