80 PROFESSOR J. C. EWART ON THE 



The trigeminal (tr.) agrees with the trigeminal of other schemes ; but as in the case of 

 the profundus, it is not represented as taking any part in innervating lateral sense 

 organs. It gives off a dorsal branch (s.o.L), and sends one branch (m.x.) in front of, and 

 a second (m.d.) behind the mouth. 



There is, however, a marked difference between the facial of this and other schemes. 

 The facial was considered by Marshall (36) as a simple and typical nerve, and it has been 

 represented as possessing a single root, a single root ganglion, and as breaking up into 

 the three typical branches, i.e., dorsal, pre- and post-branchial branches — the dorsal branch 

 forking as it proceeds forwards. In my scheme the facial is represented as arising by 

 five roots and possessing three large dorsal branches, each with a ganglion. One of the 

 roots (f.a.) lies immediately in front of the auditory nerve. This root, which has an 

 independent ganglion, and represents the facial of the higher vertebrates, breaks up into 

 four branches — a dorsal (d.f.), which passes backwards towards the first branchial cleft ; 

 a small pre-branchial (p.s.) in front of the spiracle ; a larger post-branchial (p.b.), which 

 passes behind the spiracle round the hyomandibular cartilage to proceed to the mucous 

 membrane of the mouth within the hyoid arch; and a pharyngeal (p.l.) which supplies 

 the roof of the mouth. As the post-branchial branch bends forwards, it sends a few 

 fibres to the muscles in the region of the hyoid cartilage and the jaw arches. These 

 motor branches reach a large size in the torpedo, and they represent the main portion of 

 the facial of higher vertebrates. 



Two of the dorsal branches — the superficial ophthalmic (s.o.f.) and buccal (bu.) — 

 result from the splitting of an originally simple branchial sense organ. The superficial 

 ophthalmic passes above the eyeball to supply the supra-orbital canal, and the superficial 

 ophthalmic group of ampullae. The buccal passes below the eyeball and supplies the 

 infra-orbital canal and the inner and outer buccal groups of ampullae. The third dorsal 

 branch — the segmental value of which is not yet known — runs outwards behind the 

 spiracle and supplies the hyomandibular canal and the hyoid and mandibular groups 

 of ampullae. This hyomandibular nerve has not hitherto found its way into any of the 

 schemes intended to show the general arrangement and distribution of the cranial nerves. 



The glossopharyngeal in my scheme agrees in its arrangement with that of other 

 schemes. It is represented as giving off the four typical branches. The dorsal one I 

 have represented as supplying a short part of the great lateral canal as well as a row of 

 pit organs ; but I ought to mention that though this is the distribution of the glosso- 

 pharyngeal in Amia (30), it has not yet been traced to sense organs in Selachians. 



The vagus complex, as shown in my scheme, differs very considerably from the vagus 

 of other writers. I have found it far more simple and primitive than I expected. The 

 usual plan has been to represent the vagus as made up of (1) one separate nerve with 

 a ganglion for the first vagus cleft, and (2) of a compound nerve with one large ganglion 

 made up of fibres for the three or four remaining clefts. The first nerve (vagus I.) has 

 been described as having a dorsal branch for the supra-temporal commissure, while the 

 nerve for the lateral line of the trunk has been described as springing from the large 



