THE SPINAL NERVES. 7 I 



first Spinal (r. v. d-\-c) and at the point of union there arises 

 from the second spinal the small bundle of motor fibres 

 which has been mentioned as going down to join the ven- 

 tral ramus of the third spinal. The mixed trunk now 

 gives off about six small branches of coarse fibres for the 

 depressor of the pectoral fin, two of which are drawn upon 

 Fig. 3 {dej>.) These motor fibres are derived chiefly from 

 the first spinal, though a few seem to come from the 

 second. Those from the first spinal arise certainly mainly 

 and probably exclusively from its caudal motor root, c. 



The mixed trunk now turns laterally, through the de- 

 pressor muscle and through a foramen in the scapula just 

 behind the caudal edge of the cleithrum, the fibres mean- 

 while arranging themselves in three groups, the sensory 

 fibres from the first spinal lying dorsally, the sensory 

 fibres from the second spinal ventrally and the motor 

 fibres between. The latter are derived chiefly from the 

 first spinal, though a small bundl-e from the second is in- 

 cluded. The sensory fibres from the first spinal {ctU i) 

 remain distinct from those from the second spinal and 

 pursue a very tortuous course to the skin of the side of 

 the body behind the operculum and overlying the levator 

 muscle of the pectoral fin. The cleithrum here consists 

 of two broad lamellae with the origin of the levator be- 

 tween them. This nerve runs first cephalad along the 

 outer face of the inner lamella, then laterally through the 

 muscle and then caudad along the inner face of the outer 

 lamella of the cleithrum to the skin behind the latter. 



A twig containing motor fibres from the first spinal 

 leaves the trunk at the same point as the last and supplies 

 the dorsal portion of the levator muscle (/ev.) 



The sensory fibres from the second spinal turn dorsad, 

 the remaining motor fibres from the first and second 



