28 ^AY. [Vol. IV. 



processes are joined to the strong maxillaries, which, instead of 

 being directed widely outward, as in CryptobrancJms, are turned 

 backward with their palatine processes lying close to the long 

 and strong vomers. The latter, in their turn, run far back 

 beneath the parasphenoid, and all these bones are firmly bound 

 together by connective tissue. On the upper surface of the 

 skull, too, the maxillary is closely joined to the nasal, and 

 through the prefrontal with the strongly developed frontal. 

 This, however, seems not to be enough. The premaxillary has, 

 above, a process that extends back between the nasals and ends 

 by being wedged in between the frontals for half their length. 

 Below, the premaxillary sends backward a similar spine, which 

 is firmly bound to the vomers and the parasphenoid. The pre- 

 maxillary is further strengthened by having the two backwardly 

 directed spines connected at their bases by the plate of bone 

 which functions as a partial internasal septum. The whole 

 structure of the skull is in strong contrast to that of the skulls 

 of Nectiirus and Siren, both exclusively swimming animals. 



Reference has already been made to the peculiar structure of 

 the anterior ends of the frontals, as these have been described 

 by Dr. Wiedersheim. My observations on my largest specimen 

 do not wholly confirm his descriptions. I do not find that the 

 frontal forms anything that can properly be called a ring or 

 ferrule around the escaping olfactory nerve. That the olfactory 

 nerve does leave the brain-case through the frontal is very true. 

 What I do find is this : the anterior ends of the frontals send 

 down each a descending process, which at length touches the 

 ethmoidal cartilage. For a space the processes form the side- 

 walls of the brain-case, and when they have come into contact, 

 they function as a portion of the internasal septum. Where 

 they form the walls of the cranium, the olfactory nerves of 

 course lie mesiad of them. As the processes approach each 

 other like the sides of a wedge, the nerves at length pierce them 

 and enter their respective nasal-sacs. Fig. 7 represents a sec- 

 tion made across the head at the point where the nerves are 

 either passing or are about to pass through the frontals. On 

 the right the olfactory foramen has not yet been reached, though 

 the bone is thinning. On the other side the nerve is in the act 

 of escaping through the process. Fig. 8 shows the condition of 

 things only two-thousandths of an inch further forward. Here 



