26 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. G'.) 



and also extends inward beyond the external mar<zin of the epitym- 

 panic orifice of the Aquaeductus Fallopii. The posterior surface 

 of the tuberosity slopes much more obliquely than in Delphinodon 

 dividum. 



In its general features the cerebral face of this periotic (fig. 7) 

 resembles those of DelpMnodoti dividum and Prodelph'mus. The 

 conformation of the internal acoustic meatus and associated struc- 

 tures are the chief points of difference. This meatus is broadly pyri- 

 form in outline, compressed anteriorly, and terminates in the narrow 

 slitlike channel for the passage of the facial nerve. This channel 

 leads to the entrance to the Aquaeductus Fallopii and is partially 

 closed by a slender process which projects from the pars cochlearis. 

 It is possible that other periotics will be found Avhich will have the 

 cerebral rim of the internal acoustic meatus complete as in Delphino- 

 don dividum and the narrow channel for the facial nerve will re- 

 main open as in the 

 latter, with the entrance 

 anterior to the meatus. 

 Within the meatus the 

 Aquaeductus Fallopii 

 appears to be com- 

 pressed from side to 

 side. The elongated 

 orifice of the foramen 

 singulare extends prac- 

 tically the full length 

 of the rim on the low 

 partition between the 

 spiral tract and the 

 entrance to the Aquaeductus Fallopii. The tractus spiralis foramino- 

 sus is well defined with a minute foramen centrale at the anterior 

 end, and the spiral is actually longer than in Delphinodon dividum. 

 Outside of the internal acoustic meatus and posteroexternally 

 placed is the small orifice of the Aquaeductus vestihuU, which opens 

 into a shallow triangular fossa. There is an interval of 3.7 mm. be- 

 tween it and the cerebral orifice of the Aquaeductus cochleae. The 

 cerebral orifice of the aqueduct of the cochlea is somewhat larger 

 than that for the vestibule and opens on the posterior face of the pars 

 cochlear)^ at least 2 mm. below the rim of the internal acoustic 

 meatus. On the posterior face of the periotic and above the pos- 

 terior margin of the stapedial fossa there is a shalloAV depression 

 which occupies the same area as the slitlike fossa on the periotic 

 of .Delphinodon dividum. , 



Fig. 7. — Internal or Cerebral View of Left Periotic 

 OF Kentriodon Pernix X 2. Cat. No. 8060, U.S.N.M. 



