234 THE ROYAL SOCIETY OF CANADA 



The anterior branch a soon forks again ; 1 goes to the wall of the head 

 immediately cephalad of the conjunctiva; 2 runs along the con- 

 junctiva between the head and the prothorax and sends off several 

 minute branches to the integument. Branch b is situated in the 

 anterior portion of the first thoracic segment; it gives off three 

 secondary branches as shown in fig. 4. These branches seem to in- 

 nervate the anterior portions of the longitudinal muscles of the 

 prothorax. 



2. THE THORACIC GANGLIA AND NERVES. 



There are three ganglia in the thorax, one situated in the anterior 

 portion of each segment immediately above the ventral muscles. 

 These three ganglia are similar in appearance, especially those of the 

 meso- and meta-thoracic segments. The ganglia are broadly ovate, 

 in some cases nearly globular. The size is about -7x -5 mm. The 

 pro-thoracic ganglion is joined to the suboesophageal ganglion by a 

 pair of short straight connectives about -4 mm. long. These con- 

 nectives are free throughout their entire course. The connectives 

 between the pro- and meso-thoracic ganglia and those between the 

 meso- and meta-thoracic ganglia are about 2-8 mm. long. They are 

 united for one-eighth or one-sixth of the distance from the anterior 

 ganglion, and then diverge gradually, continuing their course separ- 

 ately until they enter the anterior borders of the next ganglion. The 

 two separated connectives enclose between them a lance-shaped space 

 within which the diagonal muscles (fig. 1, dm.) cross each other near 

 their point of insertion. The median nerve of the ventral sym- 

 pathetic system leaves the connectives at the point where the latter 

 separate from each other. 



No nerves are borne by the first pair of connectives but the 

 second and third each bears a pair of nerves. 



Nerves of the First Thoracic Ganglion (figs. 1 and 2 Tl). 

 The distribution of these nerves differs from that of the second and third 

 ganglia, hence they will be described separately. 



Nerve A originates from the side of the ganglion near the anterior 

 end and runs in a lateral direction. About • 7 mm. from the origin 

 branch a is given off. It runs forward for a short distance and then 

 bifurcates, 1 running forward to innervate the ventral recti-muscles 

 in the region of the neck, and 2 running back to a diagonal muscle. 

 Branch b runs obliquely backwards and then bifurcates, each of its 

 branches innervating ventral recti muscles. Distad of the origin of 

 b, nerve A is connected with nerve b by means of a cross-nerve (g). 

 The third branch c is a small one and innervates a dorsal diagonal 



