158 NERVE COMPONENTS OF BONY FISHES. 



the spinal nerves or the spino-occipital nerves (including- 

 the hypoglossus) in all other vertebrates. See Fiir- 

 bringer ('97) for details and literature. The isolation of 

 the teleosts in this respect is striking. 



In selachians (Vetter, '78), in Ceratodus (Ruge, '97) 

 and in ganoids (Allis, '97) we have in the pre-hyal region 

 in addition to the longitudinal spinal musculature, a gen- 

 eral ventral constrictor system supplied by the V and VII 

 nerves. Now, the mm. intermandibularis, genio-hyoideus 

 and hyo-hyoideus of ganoids and teleosts have unquestion- 

 ably been derived from this ventral constrictor system of 

 selachians, as has been shown by Vetter ('78), Ruge ('97) 

 and with especial clearness by Allis ('97, p. 582, seq.) 



In the teleosts it may safely be asserted that the pre- 

 hyal " hypoglossus musculature," which in other forms is 

 supplied by the first spinal or by the hypoglossus and which 

 is known to grow forward from the post-otic myotomes, 

 is altogether absent. I think that future embryological 

 studies will confirm this and the condition is probably to 

 be explained by the overgrowth of the opercula and the 

 peculiar conformation of the isthmus. 



The so-called genio-glossus muscle of teleosts would, 

 then, not be homologous with the muscle of that name in 

 most other vertebrates. It is, however, homologous with 

 that muscle in the ganoids, for both have been derived 

 from the constrictor system and are innervated from the V 

 and VII nerves. The m. branchio-mandibularis of the 

 ganoids is a true pre-hyal ventral muscle and it is accord- 

 ingly innervated from the spinals, and all authors agree 

 that this muscle is not present in the teleosts. In the 

 bony ganoid Amia, which shows so many other teleostean 

 characters, it is significant that we find the branchio- 

 mandibularis effecting its insertion only in late larval or 



