AKT. 14. MARYLAND FOSSIL PORPOISE KELLOGG. 21 



The fenestra ovalis is relatively much larger than in Platanista, 

 oval in outline, and extends downward upon the lateral face of the 

 periotic. No stapes is present and it is evident that this element did 

 not completely fill the fenestra ovalis with its foot plate. In this 

 feature also this periotic agrees with Platanista, for in the latter 

 the foot plate of the stapes is held in position by an annular liga- 

 ment. The foot plate of the stapes completely fills the fenestra 

 ovalis in the periotic of Inia and is firmly lodged. The groove for 

 facial nerve leads directh' to the epitj^mpanic orifice of the facial 

 canal as in I?ila and thus differs from the type of groove present in 

 Platanista. Only that portion of the fossa for the stapedial muscle 

 which extends downward on the external face of the pars cochlearis 

 is preserved on this periotic, the remainder having occupied the 

 process which is missing. A characteristic feature of the tympanic 

 face of this periotic is the large swollen tuberosity on the anterior 

 process. The fossa for lodging the head of the malleus is large, rec- 

 tangular in outline, and situated in the same relative position as in 

 Platanista and Inia^ but extends inward beyond the epi-tympanic 

 orifice of the facial canal. A rather deep but narrow groove for the 

 external auditory tube appears to have been present between the 

 above-mentioned tuberosity and the posterior process. The anterior 

 end of the fossa incudis is present. 



The anterior process is rather long and is directed obliquely in- 

 ward; it is thickened dorso-ventrally and compressed laterally, but 

 its ventral and dorsal surfaces are curved and form a bluntly pointed 

 apex at the antero-ventral angle. On the external face of the ante- 

 rior process is a deep V-shaped groove or crease. An elongate con- 

 cave articular facet occupies a considerable portion of the ventral 

 face of the anterior process; this facet supports the outer lip of the 

 tympanic bone. It is possible for the uncinate process or accessory 

 ossicle of the tympanic bulla to curve around the posterior face of 

 the anterior process of the periotic (pi. 7, fig. 6), paralleling condi- 

 tions present in that of Platanista (pi. 7, fig. 5) and thus differing 

 from that of Inia. In the last mentioned genus the accessor}^ ossi- 

 cle is lodged in a depression in front of the fossa for the head of 

 the malleus. 



The resemblance between the periotic of this fossil porpoise and 

 that of Platanista is even more striking when these bones are viewed 

 from the cerebral side. The tractus spiralis foraminosus^ the cere- 

 bral orifice of the facial canal, and the foramen singulare ail lie 

 M'ithin a common fossa, which is compressed anteriorly and pyri- 

 form in general outline. The tra.ctus spiralis foraminosus is well 

 defined and ac the end of the spiral is the foramen centrale. An- 

 terior and internal to the tractus spiralis foraminosus is the cere- 



