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 accompanying 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 R. communicans from the third spinal sym- 
pathetic ganglion (com. 111), and then fuses with the Rv 
ventralis of the second spinal, as above described. 
It is thus seen that the pectoral girdle and fin of this 
specimen of the Plaice is supplied largely by the first 
spinal, but also to a certain extent by the second and 
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 RR. 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 profundus vagi, but really is only very 
closely attached to it. 
The innervation of the paired fins of Teleosts has very 
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. 
