NERVES OF THE DOGFISH 345 



trunk, being covered externally by nerve fibers (figs. 5 to 11). 

 Where the two parts of the ganglion are confluent, fibers pre- 

 dominate in the ophthalmic portion. The ventral (posterior) or 

 external mandibular ganglion is situated out on the truncus 

 hyomandibularis (figs. 20, 24, 33, and 51, guide.). It is a round 

 column of cells that does not appreciably modify the form of 

 the nerve trunk. Its root fibers run in toward the brain dorsal 

 to the root of the geniculate ganglion and ventral to the vestibu- 

 lar division of the auditory nerve (figs. 17, 31, 32, and 36, rmde.)> 

 and turning dorsally around the anterior border of the vestibu- 

 lar part of the auditory ganglion (figs. 12, 21, 22, and 24), join 

 the main lateral-line roots. 



The superficial ophthalmic and buccal portions of the dorsal 

 ganglion in Mustelus are not confluent, as in Squalus, but widely 

 separated. Both are extracranial (fig. 23). 



The shape of the anterior ganglion (oph. spf. and buc.) in 

 Squalus is modified by certain groups of cells that almost merit 

 the designation as distinct ganglia. At the dorsolateral border 

 of the buccalis portion of the anterior lateral-line ganglion, just 

 ventral to the ampulla of the anterior semicircular canal, is a 

 small conical collection of cells protruding from the general 

 mass (fig. 35, gbuc. a.). From this there pass out three small 

 nerves (only two shown in fig. 35) that supply fourteen ramuli 

 to the neuromasts of the postorbital section of the infra-orbital 

 canal. A little farther posteriorly (figs. 32 and 35), on the ex- 

 treme posterior border of the lateral-line ganglion, a more con- 

 spicuous mass of cells (got.) extends in a fashion similar to the 

 preceding. From it there pass out through a canal in the lat- 

 eral portion of the ear capsule to the top of the skull fibers that 

 supply the first five or six ramuli to the neuromasts of the main 

 lateral-line canal of the trunk. From its origin and distribution 

 this latter nerve must be regarded as the equivalent of the 

 ramus oticus of various authors. Besides innervating the lateral- 

 line canal, it supplies a peculiar tubular organ on the anterior 

 median border of the spiracle (fig. 20, ospr.). Its root fibers can 

 be traced into the acusticum by a small bundle that enters the 

 brain immediately posterior to the visceral sensory root of the 

 facialis (fig. 32, rot). 



