NERVES OF THE DOGFISH 357 



ninth nerve of Laemargus, which innervates " three sense organs 

 of the lateral line lying immediately posterior to the commis- 

 sural canal," besides sending branches to the skin. It may be 

 suggested that these latter branches possibly supply pit-organs, 

 as in Amia. In Chimaera Cole ('96) finds that from the ninth 

 "ganglion a very fine dorsal branch is sent up to the skin, but 

 this does not innervate any sense organs of the lateral line." 

 Hawkes ('06) describes a small ganglion upon the root of the 

 glossopharyngeal nerve in Chlamydoselachus from which a small 

 dorsal branch proceeds, innervating two neuromasts of the lat- 

 eral line, besides sending twigs to the skin. Allis ('01) is not 

 certain of the presence of this element in the ninth nerve of 

 Mustelus. Johnson ('17) figures various stages in the develop- 

 ment of Squalus acanthias, showing an unnamed dorsal branch 

 of the ninth nerve. In the 22-mm. stage of Squalus Landacre 

 ('16) finds in the glossopharyngeal nerve a lateral-line ganglion 

 related to two primordia and a branch of uncertain distribution. 

 Stannius ('49, p. 79) finds in Spinax acanthias and Carcharias 

 glaucus a dorsal branch whose origin, course, and distribution 

 answer to the dorsal lateral-line ramus of the ninth in Squalus. 

 He fails to find such a ramus in the rays, although a fine nerve 

 in Raja batis, a branch of the glossopharyngeus, was traced to 

 the region of the external acoustic pore. The writers confirm in 

 part the statement of Stannius that no dorsal lateral-line branch 

 of the ninth nerve occurs in the rays. In Raja radiata there is 

 no lateral-line element in the ninth nerve, nor any dorsal branch 

 of the latter. Van Wijhe ('82) states that in stage K of the em- 

 bryo of Scyllium the ninth nerve differentiates into a dorsal and 

 a ventral ramus, of which the former unites with an epidermal 

 thickening which is the anlage of that portion of the canal-organ 

 system innervated by the glossopharyngeus. In stage L the 

 glossopharyngeal ganglion begins to divide into a ganglion at 

 the base of the dorsal ramus and another on the ventral ramus. 

 Klinkhardt ('05) finds in embryos of Spinax niger a dorsal 

 cutaneous connection on the glossopharyngeus. Wright ('85) 

 mentions a dorsal lateral-line branch of the ninth nerve in Mus- 

 telus. Panschin ('10) describes a lateral-line component in the 



