EASTMAN: sharks' TEETH AND CETACEAN BONES. 89 



cochleae. AVe will now describe the different aspects of the subject 

 selected for illustration, beginning with the external. 



External face (Fig. A). — The most obvious feature of the outer lip 

 (1) of the bulla ossea relates to the presence of certain processes along 

 the superior margin. There is one at either extremity, termed respec- 

 tively iha processus anterior (3) and proc. posterior (4), whose function 

 is to unite the tympanic and petrous (2) bodies in the manner already 

 explained. These are the only points of contact where the two bodies 

 are actually fused, and they are completely separated below by the 



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V 



> 



Fig. a. — Left tyrapano-periotic uf the existing DelpMnaplerus leucas 'Pa.W&s. External 

 face, X \. 



The same numbers are used in Figs. A-F for the following parts: 1, Bulla tympanica 

 (outer lip); 2, Petrosal ; 3, Proc. ant. bullae; 4, Proc. post, bullae; 5, Proc. conicus bullae 

 (= rudimentary inferior wall forexternal auditor^' meatus) ; 6, Proc. tubarius (= partofante* 

 rior process supporting so-callfd " accessory ossicle "); 7, Proc. sigmoideus (= rudimentary 

 anterior wall of external auditory meatus); 8, Position of membrana tympani ; 9, pointed 

 anterior extremity of petrous body; 10, Proc. ant. petrosi ; 11, Proc. post, (mastoideus) 

 petrosi ; 12, Hiatus epitympanicus; 13, Aptertura extern, aquaeductus vestibuli; 14, Aper- 

 tura extern, aquaeductus cochleae; 15, Porus acusticus internus ; 16, bulla tympanica 

 (inner lip); 17, Fissura tympano-periotica; 18, Orificium (Hiatus) tympanicum ; 19, Aper- 

 tura tj'mpanica canalis Eustachii ; 20, Groove for the nervus facialis ; 21, Fenestra 

 cochleae. 



tympano-periotic fissure (IT). There are developed in the intermediate 

 space between these processes two others, the more prominent of which 

 is singularly formed, and receives the name of proc. sigmoideus (7). 

 The smaller one closely adjoining it is of conical form, and provides a 

 corresponding recess within the tympanic cavity immediately below the 

 •porus acusticus, or aperture in which the tympanic membrane is sus- 

 pended. It is numbered 5 in figures A and E, and may be referred to 



