336 Oti the Ccvlacanth Fish. 



pocket is not clear to nie, but it may liave surroundetl tlie 

 labyrinth, the outer side of the otic capsule iiaving been 

 unossified. 



Another important diffei'ence is that wliilst a foramen for 

 the seventh nerve passes through the prootic in EusthenO' 

 pferon, that of Coehicanths is imperforate. 



These comparisons show that Dr. Stensio is correct in findiiifif 

 the points of exit of the seventh and fifth nerve between the 

 sphenoid and prootic. Consideration of the position of the 

 nietapterygoid shows that he is probably also correct in 

 phiciiig the latter nerve very high up. 



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

 supraoccipital — is homologous with the ossified supraoccipital 

 region of MegaHchthys. The large posterior paired element 

 agrees closely with the exoccipital of Etisthenopttron, the 

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

 essentially for a hypoglossus. The remaining element may 

 ])robably be an opisthotic. 



Thus a fuller knowledge confirms the close similarity 

 between the neural crania of Osteolepids and Ccelacanths 

 which Dr. Stensio has shown to exist. 



The curious unossified region of the basis cranii and tlie 

 hinge in the dorsal surface which is functionally connected 

 with it are not known Cti any early bony vertebrates except 

 these forms; they are specializations nhich are s[)ecitic to 

 tlie Osteolepids, and were developed in those fish after their 

 separation from the Amphibian, Dipnottn, and Actinopterygian 

 stocks. 



Tiie occurrence of these features in a typical form in Ccela- 

 canths seeujs, in my eyes, ahnost conclusive evidence of a 

 descent from Osteolepids. 



Such descent allows us to draw most important conclusions 

 as to the kinds of structures which may be found in fi.sli 

 derived from the Osteolepids. 



As Stensio has pointed out, we have in Ccelacanths a 

 complete loss of the hyomandibular as a supporting 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- 

 su] porting bones analogous to that of Dipnoi and certain 

 LJrodeles. 



This comjiarison lends additional sujiport to the view, so 



