82 NERVE COMPONENTS OF BONY FISHES. 



it is probable that the teleosts typically possess an 

 occipito-spinal nerve a in a reduced condition. Whether 

 that nerve in Menidia has been lost or has fused with 

 d I cannot state. I have not made sufficiently extensive 

 comparative studies to speak with authority on these 

 homologies, nor have my methods been adapted for this 

 problem. 



In connection with the fact that the spino-occipital nerve 

 a, which is lost or reduced in the teleosts, is present both 

 in lower and in higher forms — as a spinal nerve in most 

 Selachii and Amphibia, and as an occipito-spinal nerve in 

 some sharks and ganoids, in Holocephali, Dipnoi and 

 many Amniota (Fiirbringer, '97) — it is exceedingly sug- 

 gestive to notice that it is the teleosts alone of all these 

 forms which lack the true pre-hyal ventral musculature. 

 The so-called genio-glossus of teleosts is supplied by the 

 trigeminus and is quite certainly not derived from the 

 hypoglossus, or ventral spinal miisculature (see the dis- 

 cussion in Section 7, IV, 5, tv), and with the loss of this 

 musculature the corresponding spino-occipital nerve has 

 naturally also suffered reduction. 



Haller ('96, p. 53) saj^s that in Salmo the spino-occipital 

 roots (his post-vagal nerve) do not participate in the in- 

 nervation of the hypoglossus musculature, but distribute 

 exclusively to the pectoral fin. The ventral musculature 

 is innervated, according to this authority, by a branch 

 from the vagus. It will probably prove that this descrip- 

 tion is inexact, and that either the vagus branch in 

 question supplies the pharyngo-branchial muscles instead 

 of the sterno-hyoideus or else that the vagus stem is 

 joined by fibres from a spino-occipital nerve which was 

 overlooked by Haller. His generalization (p, 56) that the 

 hypoglossus nerve was prihiitively included with the 

 vagus and has only secondarily been dissociated from it 

 will certainly not stand in the light of our present 

 knowledge of both higher and lower forms. 



