68 NERVE COMPONENTS OF BONY FISHES. 



crosses. Just before reaching the skin it breaks up 

 around the r. lateralis vagi to supply the muscles and skin 

 of that immediate neighborhood. 



Baudelot and many others regard the ramus medius as 

 the homologue in the spinal nerves of the r. lateralis vagi. 

 This is undoubtedly an untenable hypothesis ; and the r. 

 lateralis cannot be regarded as a collector for the spinal 

 nerves in the sense so commonly assumed. The signifi- 

 cance of this anastomosis, where it exists, is discussed at 

 the close of Section 12, I. 



The two dorsal rami are quite distinct in origin and 

 nature. One {r. com. ^), of fine fibres, arises from the 

 ganglion and, directly dorsad on the outer surface of the 

 neural arch of the vertebra, joins the ramus spinosus of 

 the third spinal nerve (r. sp. j), the compound nerve then 

 running dorsally in the intermuscular septum between 

 the general dorsal musculature and the interspinal muscles 

 (the mm. supra-carinales of Owen), where it joins the r. 

 lateralis accessorius. This nerve is the r. conniiunicaiis 

 of Stannius and is apparently exclusively sensory. The 

 other dorsal ramus (r. sp. 4) arises from the motor root 

 and is apparently exclusively motor. It effects similar 

 relations with the r. communicans of fifth spinal nerve 

 and then, as before, the mixed nerve thus formed joins 

 the r. lateralis accessorius, previously, however, sending 

 numerous fine branches into the dorsal inusculature. 

 This is the r. spinosus of Stannius. 



This, it appears from the literature, is the typical 

 arrangement of dorsal rami in fishes. (Compare espe- 

 cially, Owen, '66., Vol. I, p. 308.) The fact that the 

 cephalic one of these rami is sensory and the caudal one 

 motor would seem to be correlated with the rhythmical 

 movements of the body in swimming. Thus the sensory 



