154 



The R. medius (r. m. 3) is a mixed nerve, but largely 

 motor. It breaks up into the two branches as in the 

 second spinal, the upper one for a time aceompan}' ing the 

 intermuscular bone, and the lower the R. lateralis pro- 

 fundus vagi (but not mixing with it). 



The R. ventralis (r. v. 3) is also a mixed nerve. It 

 receives the II. communicans from the third spinal sym- 

 pathetic ganglion [com. iii), and then fuses with the R. 

 ventralis of the second spinal, as above described. 



It is thus seen that the pectoral girdle and tin of this 

 specimen of the Plaice is supplied largely by the first 

 spinal, but also to a certain extent by the second arid 

 third. It must, however, be emphasized that the limb 

 plexuses are subject to great variation, that the above 

 account is not a generalised description, and therefore 

 takes no account of variations. Stannius, however, states 

 that fibres from the RE. anteriores of the first three spinal 

 nerves pass to the pectoral fin in the Plaice. 



With regard to the fifth spinal nerve, we need only 

 mention that the R. medius arises from the R. ventralis, 

 and that its lower division appears to completely fuse with 

 the R. lateralis iDrofundus vagi, but really is only very 

 closely attached to it. 



The innervation of the paired fins of Teleosts has ver}^ 

 important theoretical bearings. In the Plaice from 

 which the spinal nerves were plotted out, the R. ventralis 

 of the fifth spinal nerve, together with that from the sixth,* 

 were the nerves which supplied the pelvic fin. Now if 

 this fin is homologous throughout Teleosts generally, 



* Stannius states that the pelvic fin of the Plaice is innervated from the 

 fourth and fifth spinal nerves, and this tallies with Cuvier's scheme. 

 In our sections, however, the fourth spinal nerve was not connected with 

 the pelvic fin. 



