FIRST TRUNCUS BRANCHIALIS VAGI. lOI 



though it is certain that most of them go to taste buds. 

 The sensory fibres of the ventral ramulus, on the other 

 hand, apparently do not go to taste buds as a rule. After 

 the first gill has joined the isthmus the dorsal ramulus 

 continues for a short distance to supply taste buds in the 

 floor of the mouth; the sensory fibres of the ventral 

 ramulus, after joining the pre-trematic ramus of the 

 first branchialis vagi, pass to similar taste buds nearer the 

 median line than the last, while the remaining motor 

 fibres separate for the m. obliquus ventralis of this gill. 

 On Fig. 3 none of the branchial ramuli of the IX and X 

 nerves are plotted for their full length except the dorsal 

 one of the IX nerve. 



The absence of the r. pre-trematicus IX (r. hyoideus) 

 is, I think, to be accounted for by the peculiar relations of 

 the pseudobranch. This structure is very large indeed 

 and occupies the whole region above and in front of the 

 first gill cleft. It, however, belongs to the region of the 

 facial; the peripheral region pertaining to the hyoidean 

 branch of the IX nerve having been thus crowded out, 

 the loss of the nerve naturally follows. Stannius reports 

 the absence of the r. pre-trematicus IX in Esox and Silu- 

 rus and its great reduction in Belone ('49, p. 76). The 

 same cause has operated also to reduce the r. pharyngeus. 

 Cole ('98a, p. 145) has shown that in the fishes, as in the 

 mammals, this ramus usually joins the visceral portion of 

 the facialis and thus is a true Jacobson's anastomosis. 

 The commissure from the IX to the VII in Menidia is, 

 however, purely sympathetic (see Section 8). 



III. — First Truncus Branchialis Vagi. 



The origin and course of this nerve from its ganglion 

 are strictly comparable with those of the glossopharyn- 

 geus. There is given off first the minute motor twig for 



