368 H. W. NORMS AND SALLY P. HUGHES 



stituents in the seventh, ninth, and tenth nerves of Hexanchus 

 and Heptanchus, but not in other selachians. Houser describes 

 and figures general cutaneous fibers in the vagus nerve of Mus- 

 telus canis. Landacre describes in the embryo of Squalus acan- 

 thias a ganglion, which he regards as general cutaneous, on the 

 vagus nerve together with a nerve which he believes to be the 

 equivalent of a ramus auricularis. In a figure prepared for the 

 first edition of Herrick and Crosby's Laboratory Outlines in 

 Neurology ('18), the writers represented the ramus dorsalis of 

 Squalus as containing somatic sensory fibers. The true relations 

 are shown in the second edition ('20, fig. 5). Besides fibers term- 

 inating in canal organs, there were other constituents of the ramus 

 dorsalis that ended in the skin, losing for the most part their 

 myelin near their termination. More careful examination has 

 shown that in every instance such fibers of the ramus dorsalis 

 terminate in pit-organs. The writers are forced to the conclu- 

 sion that in Squalus acanthias there is no general cutaneous com- 

 ponent in the vagus nerve of the adult and late embryonic con- 

 dition. Careful search has revealed no connections between the 

 tractus spinalis trigemini and the vagus nerve. Nor can there 

 be found any ganglia in the vagus nerve of Squalus except the 

 three lateralis ganglia and the four (five) ganglia on the branchial 

 and intestinal nerves. 



The occurrence of well-defined somatic sensory components in 

 dorsal branches of the vagus nerve in ganoids and teleosts (Her- 

 rick, '99, '00, '01; Allis, '97; Panschin, '10) leads to the expec- 

 tation of finding them in the selachians. It may be that the 

 condition in Squalus is not typical. The finding of a somatic 

 sensory ganglion by Landacre in the embryo suggests that its 

 occurrence may be general. 



Hawkes notes that two kinds of fibers are found in the dorsal 

 branches of the ninth and tenth nerves of Chlamydoselachus : 

 coarse fibers, interpreted as lateral-line, and " smaller medullated 

 fibers probably general cutaneous." The writers have observed 

 that the pit-organs in Squalus are innervated by fibers of notice- 

 ably smaller caliber and less dense medullation than those supply- 

 ing the canal organs. 



