44 PKOOEBDINOS OF THE ACADEMY OF [1894. 



Mail has no significance, since in Man and mamtnals generally there is 

 always a small portion of the alisphenoid behind the foramen ovale, 

 amounting, indeed, in the sheep to about one- half the bone. 



The statement often made that the bone lying behind the exit of 

 the fifth nerve is the homologue of the upper part of the human pars 

 petrosa is simply not correct so far as concerns Man and mammals. 



In view of the facts just mentioned some anatomists have con- 

 sidered the bone No. 6 in the fish as the homologue of the alisphen- 

 oid in Man and have so named it. Other anatomists, on the other 

 hand, impressed with the fact that the bone su})ports a part of the 

 membranous labyrinth, have regarded it as the homologue of the 

 upper part of the human pars petrosa and called it accordingly pro- 

 otic. In the judgment of the author an insuperable objection to 

 accepting the latter view is that it involves the inevitable but absurd 

 conclusion that its homologue, or the prootic portion of the pars 

 petrosa, must transmit the superior and inferior maxillary branches 

 of the fifth nerve. On the other hand, it might be urged that the 

 bone No. 6 cau not be the homologue of the alisphenoid in Man 

 since the latter never supports any part of the membranous labyrinth. 

 In reply to the latter objection, though at the risk of committing a 

 petitio priucipii, the author must say that it is just in this respect 



that the skull of the cod- 

 fish differs from that of 

 INIan : The bone No. 6, 

 in the fish, the homo- 

 logue of the alisphenoid 

 in Man, protects the an- 

 terior part of the laby- 

 rinth as is done by the 

 upper part of the human 

 pars petrosa, the differ- 

 ence being conditioned 

 by the part of the mem- 

 branous labyrinth being 

 Fig. 9. Interior view of auditory region of alligator, relatively enormously 



developed in the fish, the osseous covering but little so, whereas in 

 Man the labyrinth is but little developed while the pars petrosa is 

 much so. 



If this view be correct then the bone No. 6 in the fish 

 must be regarded as the hoinologiu! of the alisphenoid in Man 



