394 HOWARD AYERS 
What the distribution of these several elements through the 
net is, has not been made out. It is notable that so many brain 
centers have established connection with the sensory outposts 
of the anterior end of the head, and that the muscles of the jaw 
apparatus are closely tied up with this mechanism, as also are 
the eye and nose. . 
TO SUM UP THE NERVES 
In Amphioxus the five nerves of the jaw apparatus arise seg- 
mentally and evenly spaced from a long section of the central 
nervous system and run to the walls of the buccal chamber, the. 
jaw apparatus and its tentacles, the velum and the cheeks and 
lips of the buccal region. Here they form nets or plexuses, the 
most extensive of which surround the jaw bars and their muscles 
and extend part way out on the tentacles. The nerves from the 
right and left sides also anastomose freely. ‘Thus the parts of 
the jaw apparatus and the walls of the buccal cavity are tied 
together as a physiological or operating unit, and this extensive 
peripheral intercommunication may be an expression of the lack 
of a similar central mechanism and an effort to make good the 
deficiency. ‘The jaw nerves are thus tied together peripherally 
more intricately than we yet know them to be centrally. The 
whole of the jaw apparatus is used in the work of food collec- 
tion more or less passively. 
In Bdellostoma the origins of the five nerves are crowded 
together by the condensation of the long segment of the spinal 
cord of Amphioxus into a short section of the spinal brain, the 
medulla. They all leave a projecting lobe of this spinal brain 
with their root bundles more or less intermingled, but still rec- 
ognizable as separate nerves. They all run to the Jaw appara- 
tus, which has been separated into two distinct parts, one of 
which is put into active use in food gathering in a predacious 
manner, and the rest of the skeleton of the jaw apparatus is 
left for the passive work of a supporting skeleton for parts of 
the mouth having little motion. 
Arriving in the territory of the jaw apparatus, the nerves 
intercommunicate by extensive anastomoses to build a plexi- 
