THORACIC GANGLION 



33 



from above the middle of the mesothoracic ganglia. The doisal 

 regions of the mesothoracic and metathoracic ganglia show gangli- 

 onic swellings. From the antero-dorsal sides of the prothoracic 

 ganglia a pair of prothoracic dorsal nei'ves (pr.d.) arises and su])plies 

 the muscles of that rejjion, includin>j those of the anterior thoracic 

 spiracle. The nerves supplying the mesothoracic legs (ms.ci\) 

 arise from the postero-ventral sides of the mesothoracic ganglia. 

 Between the mesothoracic ganglia there is a median ganglionic 



-ms.cr 



Fig. 10. Thoracic compound ganglion aftei' the removal of the cortex. Seen from 

 the ventral side. This and fig. 9 were drawn from models reconstructed from 

 sections. 



Pr.G., Ms.G., Mt.G. Pro-, meso-, and meta-thoracic ganglia. A.G. Abdominal 

 ganglion. Other lettering as in fig. 8. 



mass, situated slightly dorsal, from the middle region of which 

 the nerve fibres of the large pair of dorsal mesothoracic nerves 

 (ms.d.) arises ; Lowne, in the blow-fly, calls these prothoracic. 

 The roots of these nerves are broad dorso-ventrally. These nerves 

 innervate the stemo-dorsales muscles of the middle region. In 

 this median mesothoracic nerve centre, posterior to the origin 

 of the dorsal mesothoracic nerves, the fibres of a pair of nerves, 

 the accessory dorsal mesothoracic nerves (ac.ms.), have their 

 origin ; externally these appear to arise dorsal to the roots of 

 the mesothoracic crural nerves. The dorsal metathoracic nerves 



3 



n. H.-F. 



