336 On the Ccelacanth Fish. 



pocket is not clear to me, but it may have surrounded tlie 

 labyrinth, the outer side of the otic capsule having been 

 unossitied. 



Anotlier inipoitant difference is tliat wliilst a foramen for 

 the seventh neive passes through the prootic in Eustheno- 

 pferon, that of CcElacanths is imperforate. 



These comparisons show that Dr. Stensio is correct in finding 

 the points of exit of the seventh and fit'tii nerve between the 

 sjjheuoid and jjrootic. Consideration of the position of the 

 nietapterygoid shows that he is probably also correct in 

 phiciiig the latter nerve very higii up. 



Of the other three elements of the brain-case, one — the 

 supiaoccipital — is homologous with the ossified supraoccipital 

 region of Megalichthys. The large posterior paired element 

 agrees closely with the exoccipital of Eiisthenopttron, the 

 foramina piercing it being for two occipital nerves — that is, 

 essentially for a hypoglossus. The remaining element may 

 jirobably be an opisthotic. 



Tims a fuller knowledge confirms the close similarity 

 between the neural crania of Osteolepids and Coelacanths 

 which Dr. Stensio has shown to exist. 



The curious unossified region of the basis cranii and the 

 hinge in the dorsal surface which is functionally connected 

 with it are not known in any early bony vertebrates except 

 these forms; they are specializations %\hich are specific to 

 the Osteolepids, and were developed in those fish after their 

 separation from the Amphibian, Dipnoan, and Actinopterygiau 

 stocks. 



The occurrence of these features in a typical form in Coela- 

 canths seems, in my eyes, almost conclusive evidence of a 

 descent from Osteole{)ids. 



Sucii descent allows us to draw most important conclusions 

 as to the kinds of structures which may be found in fish 

 derived from the Osteolepids. 



As Stensio has pointed out, we have in Coelacanths a 

 complete loss of the hyomandibular as a sup))orting element 

 of the jaw. This loss is an exact parallel to that which has 

 occurred in Tetrapods and Dipnoi. 



We have a separation of the teeth from the bones to which 

 they were formerly attached and their fusion into independent 

 ossicles, which is exactly parallel to that which occurs in 

 many Actinopterygians (e. g., Amia). 



We have a great reduction or loss of the external tooth- 

 supporting bones analogous to that of Dipnoi and certain 

 Urodeles. 



This comparison lends additional suj'port to the view, so 



