ORIGIN OF JAW APPARATUS aH3 
nerves from the central nerve cord which lie between the second 
nerve—the septalis—and the velum. These five nerves are the 
nerves of the jaw apparatus and velum, supplying also the walls 
of the buccal cavity and the other organs connected therewith, 
besides giving branches to the skin and myotomes. My own 
_ repeated studies of the head nerves of Amphioxus are in agree- 
ment with the major facts which may be classed as well estab- 
lished. There is great flexibility in the arrangement of the 
nerves of the head. The septal nerve and the eighth may also 
take part in the nerve supply of the jaw apparatus, but this is 
not usual. 
The frequent presence of unusual dorsal roots and the occa- 
sional absence of one of the important visceral trunks are purely 
individual variations, and do not affect the large facts of the 
nerve supply of the jaw apparatus which are given here in con- 
densed form for convenience of comparison with the nerve supply 
of the jaw apparatus of Bdellostoma. 
An accurate drawing of the five nerves of the left side control- 
ling the jaw apparatus, together with a posterior ventral branch 
of the septal nerve and the first postmandibular nerve or the eighth 
nerve counting from the terminalis, is shown in figure 12. The 
course of the visceral branches over the myotomes, and the 
larger branches to the jaw apparatus are accurately drawn. There 
is great variation in method of branching in different individuals, 
but this figure is typical for Amphioxus lanceolatus. The velar 
nerves are not drawn in, and only one of the deep branches turn- 
ing mesad under the ventral edge of the body muscle is partly 
shown. In general these nerves show only a slight tendency 
to run cephalad, most noticeable where the ventral branches 
emerge from behind the myotome. Their general course is nearly 
due ventrad to their terminals, which in Amphioxus is the plexi- 
form nerve net described by Fusari, Dogiel, and Kutchin as con- 
sisting of three main sections, an inner and outer jaw bar plexus 
and a more or less distinct tentacular plexus. From the plexiform 
structures the final terminal nerves are given off. The plexi- 
form structures are associated with a longitudinal nerve trunk 
composed of a number of relatively large nerves running the 
