24 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. GO 



and Prodel/phinus longirostris (Cat. No. 21168, U. S. N. M.) in that 

 the ventral surface is inflated more noticeably between this facet and 

 the fenestra rotunda, forming an indistinct transverse crest, to the 

 putside of which is a shallow concavity which slopes to the fenestra 

 ovalis, and to inside is a slightly convex surface which slopes for- 

 w,ard and inward. The fenestra rotunda is a subtriangular in out- 

 line and is slightly larger than the fenestra ovalis. A slight swelling 



is developed on the poste- 

 rior face of the periotic 

 above the fenestra rotunda 

 which does not appear to 

 have any relation to the 

 aqueduct of the cochlea. 

 The foot plate of the 

 stapes completely fills the 

 ovoidal fenestra ovalis and 

 is held in position by a 

 pair of narrow internal 

 ledges which extend across 

 the anterior and posterior 

 walls, respectively. With- 

 in the vestibule are the ori- 

 fices of three small canals, 

 the largest of which are 

 situated opposite to the 

 epitympanic orifice of the 

 Agnaedticfus Fallopii and 

 lead to the semicircular 

 canals ; the other, a minute 

 orifice, is situated at the 

 posterointernal angle and 

 is the terminus of the 

 aqueduct leading from the foramen singulare. On the internal wall 

 there is a small passage which leads into the scala vestibuli. The 

 ei^itympanic orifice of the Aquaeductus Fallopii is small and the 

 narrow groove for the facial nerve, which leads from it, is sharply 

 defined between the rim of the fenestra ovalis and the projecting 

 ledge for the fossa incudis, but posterior to them it follows along the 

 internal face of the posterior process to the posterior angle. A con- 

 tinuous thin-edged crest extending from the epitympanic orifice of 

 the Aquaeductus Fallopii to the pars cochlearis separates the rim of 

 the fenestra ovalis on outside from the groove for the facial nerve 

 and on the rear from the fossa for the stapedial muscle. The elongate 

 fossa for the stapedial muscle is rather deep, concave from side to 



Tig. 6. — Ventral or TvMpanic View of Left Peri- 

 otic OF Kentriodon peknix. X 2. Cat. No. 8060, 

 . .U.S.Nat.Mus. The Same Numbers are Used on 



' Figures 6 and 7 for the Following Struc- 

 tures : 1, Fenestra Rotunda ; 2, Fenestra 

 Ovalis ; 3, Cerebral Orifice op Aquaeductus 

 'Cochleae; 4, Cerebral Orifice of Aquaeductus 



. Vestibuli ; 5, Processus Anterior Petrosi ; 6, 



Fossa for Head of Malleus; 7. Semiclosed 



; Canal for Facial Nerve; 8', Epitympanic Orifice 



OF Aquaeductus B'allopii ; 9, Fossa for Stape- 



• DIAL Muscle ; 10, Processus Posterior Petrosi 

 (Mastoid Process, in Part) ; 11, Internal Acous- 

 tic Meatus ; 12, T'oramen Centrale ; 13, Foramen 



: Singulare ; 14, Entrance to Aquaeductus Fal- 

 lopii ; 15, Fossa Incudis 



