KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. 587 



et van der Stricht ('98, p. 36) state that the plexus of Fusari is formed 

 from branches of left dorsal nerves III-VI, and perhaps VII. As has 

 been stated, a branch of left ner^-e V usually anastomoses with a 

 branch, or branches, of left nerve \ I. From this anastomosis a branch 

 passes to the velum, frequently uniting- in its course with a branch of 

 left nerve VII (Fig. 7). This branch to the velum may divide in 

 various ways before entering the latter structure. Its branches, 

 however, enter the \-elum on the left side of the body. 



Xcrve VII. — Figure 6 (PI. 2) shows this nerve leaving the neural 

 tube slightly nearer its dorsal surface than nerve VI. The dorsal 

 ramus of nerve VII on either side of the body is similar to that of nerve 

 ^T, except for a slight increase in size, due to the larger territory lying 

 dorsal to the seventh nerve root. The ventral ramus of nerve ^TI on 

 either side of the body does not differ from that of nerve VI in the 

 region of the trunk muscles. Right nerve VII sends one or more 

 branches to the posterior portion of the outer mouth plexus. These 

 branches give off small side branches in their coui-se across the oral 

 hood. Nerve VII of the right side occupies a position considerably 

 posterior to that of left nerve VII, and its ventral ramus frequently 

 lies exterior to the velum. In such cases right nerve VII is usually 

 the most posterior ner\e of the right side sending branches to the outer 

 plexus of the mouth border. In nearly all the specimens examined 

 the branches of left ner\'e VII were found to be exclusively cutaneous 

 in their distribution . This nerve sends branches to the outer mouth 

 plexus of the left side, similar to the corresponding branches of right 

 nerve VII. I have been unable to find a branch, or branches, of left 

 nerve VII in either species directly connected with the inner plexus of 

 the mouth border. As has been noted, Heymans et van der Stricht 

 ('98) state that left nerve VII is perhaps concerned in the formation 

 of the plexus of Fusari. This may be the case in rare instances, but is 

 certainly not the usual condition. These authors also state that left 

 nerve VII contributes toward the innervation of the velum. Dogiel 

 ( : 02) also says that nerve ^ II not infrequently takes part in the inner- 

 vation of the velum. The specimens examined by me revealed no 

 large branches of left ner\'e ^TI passing directly to the velum. In a 

 few cases a small branch, or branches, of this nerve anastomosed with 

 branches of left nerve V or VI (Figure 7) ; therefore fibers from branch 

 VII may take this course to the velum; but it is difficult to determine 

 the course of nerve fibers after such an anastomosis. 



Nerve VIII. — This nerve will be briefly considered here, although 

 its branches, for the most part, supply the branchial region. It may 



