3l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



lateral of the two branches extends only half of the length of the 

 tibia. The mesal one branches twice to provide three nerves, one of 

 which is closely afifixed to the apodeme of the retractor of the claws. 

 A second branch innervates the levator of the tarsus (io8) and the 

 depressor of the tarsus (109), then continues along the ventral wall 

 of the tibia. The third branch proceeds along the dorsal wall of the 

 tibia. Within the tarsus, the ventral nerve ends in profuse branches 

 along the cuticular wall, while the remaining two nerves pass over the 

 unguitractor plate and each terminates within a claw. 



V. THE CERVIX AND THE PROTHORAX 



The cervix or neck of insects is presumably derived in part from 

 the labial segment and in part from the prothoracic. Accordingly, 

 the musculature of the cervical region is believed to have evolved 

 from muscles of both the labial segment and the prothorax. The con- 

 cept that the muscles of a segment are innervated from the ganglion 

 of that segment suggests that each muscle of the cervix can be assigned 

 to one or the other of these segments simply by determining the seg- 

 ment of innervation of each. 



Three pairs of nerves enter the cervix from the suboesophageal 

 ganglion, one pair of which is joined by a pair of nerves from the pro- 

 thoracic ganglion. An examination of figures i and 3 shows that 

 the nerve from the prothorax is obviously a counterpart of the dorsal 

 nerve of the mesothorax and metathorax, and that the nerve joining it 

 from the suboesophageal ganglion is the anterior ganglionic connec- 

 tive of the prothoracic dorsal nerve. The anterior connective is 

 markedly more robust than is the dorsal nerve itself as it leaves the 

 prothoracic ganglion. 



The muscles innervated by the prothoracic dorsal nerve presumably 

 include the dorsal longitudinal muscles of the prothorax. However, 

 of the dorsal muscles, only the tergopleural intersegmental muscle 

 (58), extending from the protergum to the mesepisternum, is clearly 

 innervated by the prothoracic dorsal nerve alone. The first and the 

 second protergal muscles of the head (47, 48) are innervated by the 

 second of the nerves entering the cervix from the head, here called 

 the second cervical nerve, as well as by the dorsal nerve of the pro- 

 thorax. These two muscles may therefore represent a fusion of the 

 dorsal longitudinal muscles of the labial segment and the prothoracic. 

 The longitudinal dorsal muscle of the neck and prothorax (49) and 

 the dorsal lateral neck muscle (56) receive innervation from only the 

 second cervical nerve. 



