BOWERS. — CRANIAL NERVES OF SPELERPES BILINEATUS. 191 



The last branch from the IX. -f X. complex to be described is (k) 

 ramus visceralis (X. rm. vsc). It has been left in neutral tint to the 

 point of branching, for the same reason that was given for r. hyoideus. 

 It leaves the latero-caudal angle of the ganglion ventral to the lateral- 

 line nerves, and curves ventrad. It is composed of deeply staining and 

 of unstained fibres. Part of the latter are given off in the first branch 

 (X. rml. vsc. oe.), which was followed caudad to the region of the oesoph- 

 agus. Other branches, not plotted in the drawings, were given off 

 mesiad from the region in which the nerve separates into two motor 

 branches (Fig. 1). One of these motor branches (rm. lar.) curves 

 cephalad, followiug closely the course of the hypoglossus for a short dis- 

 tance. It is distributed in part to a transverse sheet of muscles below 

 the pharynx, which Wilder ('91, p. 188) interprets as resulting from a 

 fusion of digastricus pharyngis and dorso-laryngeus. Spelerpes, being 

 a lungless form, has no use for the laryngotracheal muscles as such. 

 Wilder maintains that they are employed to form this pharyngo-oeso- 

 phageal sheet. The distribution of the remaining portion of this branch 

 is to the constrictor arcuum branchiarum. This branch would therefore 

 seem to be r. laryugeus, although it issues from the ganglion with r. 

 visceralis. 



The other motor branch (rm. scap. ?) was traced caudo-ventrad to the 

 region of the shoulder girdle, and is perhaps the r. scapularis of Fiir- 

 bringer. 



G. First and Second Spinal Nerves. 



(!) The first spinal nerve in Spelerpes bilineatus arises by two ventral 

 roots, which run cephalad a short distance after they emerge from the 

 brain, then pass through the cranial cartilage and divide into two 

 branches, — a dorsal (rm. d. spi-i), which goes to m. longissimus dorsi, 

 and a ventral (rm. v. s/n'.i), which curves caudad, ectad, and then ventrad, 

 finally corning into such close relation with the hypoglossus that the two 

 appear, even when cut transversely, as one nerve. The two remain 

 together for a short distance, then the first spinal curves mesiad and 

 cephalad ; it was traced to the mesial surface of m. sterno-hyoideus, but 

 fibres were not seen to actually enter that muscle. 



(2) The second spinal nerve was found to have a ventral root (rx. v. 

 spi. 2 ) similar to that of the first, and also a well-developed dorsal root 

 (rx. d. spi. 2 ). Kingsbury ('95. p. 149) says, "The hypoglossus in Am- 

 phibia is generally described as formed by the union of the ventral trunks 

 of the two nerves arising immediately caudad of the vagus group, to 



