118 



PROCEEDINGS OF THE NATIONAL MUSEUM 



The ventrointernal border of this facet projects inward and contrib- 

 utes the floor for the facial canal. A rather distinctly margined 

 subpyriform excavation, which is located on the internal side and at 

 the base of the ventral surface of the anterior process, constitutes the 

 fossa for the reception of the head of the malleus. In contrast, the 

 corresponding fossa on the left periotic associated with the skull is 

 shallower. 



The fossa incudis occupies the same location as on the left periotic, 

 but is narrower and more elongated and is continued downward on the 

 anteroexternal angle of the posterior process. 



On the cerebral face of this right periotic (pi. 5, fig. 5) the internal 

 acoustic meatus is somewhat compressed from side to side and 

 elongated, and terminates in a narrow slitlike channel for the passage 

 of the facial nerve. This channel leads to the entrance of the aquae- 

 ductus Fallopii and is slightly constricted medially by a narrow lip 

 projecting from the pars cochlearis. The small orifice for the foramen 

 singulare is situated posterior to the low osseous ridge between the 

 spiral tract and the entrance to the aquaeductus Fallopii. 



The tractus sphahs foraminosus is well defined with a minute 

 foramen centrale at the anterior end. Outside and posteroexternally 

 to the rim of the internal acoustic meatus is the small orifice of the 

 aquaeductus vestibuli that opens into a deep ovoidal fossa. There 

 is an interval of 4.2 mm. between it and the cerebral orifice of the 

 aquaeductus cochleae. The cerebral orifice of the aqueduct of the 

 cochlea is slightly larger than that for the vestibule and opens into 

 the groove on the posterior face of the pars cochlearis at least 3 mm. 

 below the rim of the internal acoustic meatus. On the posterior face 

 of the periotic and above the posterior margin of the stapedial fossa 

 there is a shallow circular depression approximately 5 mm. in diameter. 



Measurements of the periotics (in millimeters) 



