}24 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



IX. THE MEDIAN NERVES AND THE INNERVATION OF THE 

 SPIRACULAR MUSCLES 



The median or unpaired nerves of the pregenital abdominal seg- 

 ments following the second in Dissosteira are shown in figure 5 A. 

 In these segments, a transverse or lateral nerve leaves the median 

 nerve and extends into the segment on each side, as is usually figured 

 in descriptions of the median nerve system. The definitive end of 

 this lateral nerve joins a larger nerve which branches anteriorly from 

 the dorsal nerve of the posterior segment. The dilator muscle (dlsp) 

 and the occlusor muscles (osp) of the spiracle of the posterior seg- 

 ment are innervated by a branch arising from this anterior branch. 



-Gng- — 



Fig. 5.— Diagrams of the nerve patterns of the right side of typical pregenital 

 abdominal segments, viewed mesally. A, Dissosteira. B, Diaphcromcra. 



In the walkingstick (fig. 5 B), the cricket, and the cockroach, a 

 similar connection of the transverse nerve with the dorsal nerve and 

 the innervation of the spiracles occurs. Maki (1936) found a similar 

 condition in the abdominal segments of Chaiiliodes. The existence 

 of a definitive connection of the transverse nerve with the dorsal 

 nerve thus occurs in both the Orthoptera and the Neuroptera. 



In the thorax of Dissosteira, a complete median nerve was found 

 extending from the suboesophageal ganglion to the prothoracic, but 

 not between the remaining thoracic gangUa (fig. 2). A single nerve 

 arises dorsally from the prothoracic ganglion and, passing above the 

 ventral longitudinal muscles, joins the branch of the mesothoracic 

 dorsal nerve which provides innervation of the muscles of the first 

 spiracle and the sternopleural intersegmental muscle (59), and be- 



