232 THE ROYAL SOCIETY OF CANADA 



lies in the fact[thatin the[thorax F the_;first:pair of connectives are quite 

 separate and the second and third pairs^are united for a very short 

 distance, while in the abdomen the connectives, which are united 

 throughout the greater part of their course, separate shortly before 

 entering the posterior ganglion. 



The mandibles, maxillae, labium and the anterior portions of 

 the silk glands are innervated by the suboesophageal ganglion. The 

 description of the nerves of this ganglion follows. 



The Mandibular Nerve (Fig. 4, Md.). This is the largest nerve 

 of the suboesophageal ganglion as might be expected from the fact 

 that the mandibular muscles are the largest and most numerous in 

 the head. It is given off from the anterior border of the ganglion, 

 inside of the insertion of the crus. It runs forward, beneath the 

 pharynx for a short distance. Emerging from beneath the pharynx, 

 it runs towards the back of the head and then bends outwards passing 

 beneath the dorsal layer of the large adductor muscles of the mandible. 

 It then turns backwards, its branches ramifying among the mandi- 

 bular muscles. 



The mandibular nerve gives off a large number of branches, the 

 chief of which are described below. 



Branch a is given off a short distance from the origin, and pro- 

 jects forward beneath the pharynx, terminating near the base of the 

 labium. It gives off two branches which go to muscles of the labium. 

 Branch b originates back of the tentorium and partially innervates 

 the large adductor muscle of the mandible. The third branch c arises 

 nearly opposite to 6. It extends forward entering the base of the 

 mandible where it innervates certain small muscles. The next branch 

 d also extends forward into the mandible where it divides into several 

 branches. Shortly after giving off d the mandibular nerve bifurcates, 

 the branches (e and f) both run back to the base of the mandibular 

 muscles near the neck of the insect. The two branches run parallel 

 to each other, e above /.with a layer of muscle interposed between them. 

 They both give off numerous branches, as shown in fig 4, which 

 ramify among the mandibular muscles. 



The Maxillary Nerve (fig. 4, Mx.) arises from the ventral side of 

 the anterior end of the ganglion and runs forward, innervating the 

 maxilla and its muscles. 



The proximal branch a soon bifurcates innervating certain of the 

 maxillary muscles. It is also connected with branch r of the lateral 

 sympathetic system. Branch b runs obliquely towards the integu- 

 ment where it terminates in a minute ganglion from which several 

 small sensory nerves arise. Distad of the origin of b four branches 

 c are given off close to each other and all innervate maxillary muscles. 



