1906.] NERVES OF CHLAMYDOSELACHUS AXGUIXEUS. 987 



branch (text-fig. 141, D.B.) before uniting with the dorsal, ganglio- 

 nated root. In the anterior and middle regions of the vertebral 

 column, this union takes place at a level with the top of the 

 notochord, but in the tail-region at a level with the base of the 

 notochord, immediately to the inner side of the r. lateralis vagi. 

 The ventral branch (V.B.) is given off at varying points (text- 

 fig. 141). 



The dorsal branch (D.B.) of the ventral root runs caudad and 

 upwards, passing over the ganglion of the dorsal root (D.R.G.) to 

 be distributed to the muscles of the middle region of the back. 

 A similar I'oot (ventral-doi'sal) has been described by Ewart and 

 Cole in Raia (6. p. 479). No dorsal branch was found for the 

 complete spinal nerve or for the dorsal i-oot, as it is pi'obable that 

 the dorsal branch of the ventral root receives fibres from the 

 doi'sal root as it passes ovei- the latter on its backward course. 

 In one segment (text-fig. 141) the dorsal branch of the ventral root 

 could be seen by the naked eye running over the dorsal root- 

 ganglion, from which it could not be separated ; in the succeeding 

 segment the dorsal and ventral roots were joined in the region of 

 the sensoiy ganglion, and the dorsal bi-anch appeared to aiise from 

 the ganglion itself. The spinal nerves here recall the condition of 

 Lcemargus (6. p. 480), of Bdellostoma (16. p. 176), and of Myxhie *, 

 in that all three have (1) several rootlets for the ventral root, 

 (2) a dorsal branch from the ventral root which unites with the 

 dorsal root-ganglion or with some portion of the dorsal root. 



I A. The Brain. 



The external featvu^es of tlie brain, having a typical arrange- 

 ment, need not be described. Two drawings, however, are given 

 (PI. LXIX. figs. 7 & 8) as those of Garman are not clear. His 

 ventral view is inaccurate, owing to the very badly-preserved 

 condition of liis specimen. 



Two points only may be noticed : (1) there is a large rhinocoel 

 extending to the end of the olfactory stalk ; (2) the dorsal roof of 

 both prosencephalon and i-hinoccel is non-nervous. This second 

 point is of considerable interest, as it recalls the condition of 

 Ammoccetes and of the Teleosts. The non-nervous roof may be 

 regarded as primitive when compared with that of A^nmocoetes, 

 but as specialised when compared with that of the Teleosts. That 

 a non-nervous roof should be found amongst the Elasmobranchs 

 is a point of considerable interest, although its significance is as 

 yet undetermined. 



I B. Locy's Nerve. 



Locy's nerve, which is present in Chlamydoselachus, oi-iginates 

 near the middle line, somewhat to the ventral side of the fore- 

 brain. It passes outwards, curving upwards along the anterior 

 and upper side of the olfactory stalk to be distributed between 



* Mr. Cole kindly showed me some unijublished drawings of the spinal nerves of 

 Myx ine. 



