LATERAL CANAL SYSTEM OF SELACHIANS 27 



As far as I am aware no observations have been published on 

 the peripheral terminations of the lateral nerve in selachians and, 

 as indicated above, the work on other forms has not been en- 

 tirely satisfactory. The following account is based on the study 

 of a great number of preparations made from successfully im- 

 pregnated sensory epithelium from the lateral canal of Muste- 

 lus canis. In order to disclose all pos.sible relations, sections 

 were cut transversely, obliquely, and longitudinally, to the 

 long axis of the canal, and a few were cut in a plane at a right 

 angle to the long axis of the hair-cells. 



It has already been stated that each ramulus of the lateral 

 nerve approaches the sensory canal obliquely (figs. 4, 13) and 

 that the sensory column is developed on the medial superior wall 

 of the canal. What is spoken of as the base of the sensory 

 column is thus directed towards the superior boundary wall of 

 the sensory canal (fig. 6). 



Each ramulus of the N. lateralis is composed of eighteen to 

 thirty or even more nerve fibers, varying in diameter from one 

 to .six micra (figs. 14, 15). The majority of the fibers are medul- 

 lated and they are bound together by a comparatively thick 

 connective tissue sheath. Upon reaching the base of the sen- 

 sory column the outer sheath of the ramulus merges into the 

 dermal tissue surrounding the sensory canal and the nerve 

 fibers then pass in both directions, i.e., caudad and cephalad, 

 along the sensory column outside the basilar membrane (fig. 5). 

 The nerve fibers from adjacent ramuli overlap for a short dis- 

 tance on the base of the sensory colunm. A continuous and 

 well-marked fiber zone is thus formed which extends throughout 

 the length of the sensory column, Natiu-ally this fiber zone is 

 largest where the ramuli first reach the canal, and smallest 

 approximately midway between two adjacent ramuli, where 

 fibers from each territory overlap for a short space (figs. 5, 12). 

 In no case has a complete break in the continuity of the fiber 

 zone been observed. This condition is similar to an old sketch 

 of Hexanchus griseus published in 1859 in Leydig's Lehrbuch 

 der Histologie. 



