PLATANISTA. 



521 



of the process, runs a very distinct groove ending posteriorly in a faintly marked 

 tubercle representing the manubrium. It seems as if the groove was homologous to 



Fig. 18. 



Magnified views of small ear bones of Platanista. 



A, left malleus. B, right malleus from opposite side. C, the incus. 



the outer surface of that process in other orders of the mammalia, the hooked or 

 blunt point corresponding to the processus brevis. Many of the fibres of the 

 fleshy prolongation of the membrana tympani to the malleus are attached to the 

 bottom of that groove and are often seen still adherent in imperfectly dried speci- 

 mens." In Monodon and the dolphins proper, some of the fibres are in the same 

 manner inserted along the head of the malleus, as well as to the splinter-hke, more 

 definite homologue of the manubrium.^ 



The processus longus of the incus is as thick as in Monodon, and the articular 

 surface for the head of the stapes is as small ; the posterior crus is even less 

 developed than in Delphinus. The stapes is of the same form as in the smaller 

 dolphins, without a trace of any interneural aperture^ ; there is sometimes a large 

 tubercle for the stapedius tendon on the inner aspect of the head. 



Vomer (PL XL, fig. 1, vo). — This is directed downwards and forwards, but 

 has a twist to the left side. It may be resolved into three portions : 1st, the ex- 

 panded plates which invest the under surface of the orbito-sphenoid and a portion 

 of the basisphenoid ; 2nd, the thin nasal plate between them ; Srxl, a division 

 consisting of two wings, between which the mesethmoid cartilage {me) is received, 

 the latter terminating below and anteriorly in a thin vertical plate wedged between 

 the vertical plates of the maxillae, the posterior extremities of wliich are applied 

 to a lateral expansion on its posterior border. 



The expanded plates are broad and form the posterior wall of the nasal canal. 

 At the middle of their external margins there is a pointed process projecting down- 

 wards and outwards and which interposes between the palatine and pterygoid, and 

 above this process the palatine is articulated to the rough surface on their thick 

 external margins, and below it the nasal surface of the pterygoid is applied to the 

 remaining portion of their external margins which bend inwards, terminating, in 

 the adult, in a more or less truncated posterior margin. The upper borders of the 



' In making a fresh dissection of the tympanum of this dolphin, I have found a strong band of fibres inserted 

 into the groove, and the tensor tjmpani was inserted into the depression above described. 



- In the stapes of a young Susu there is a well-defined and rather large interneural aperture, but in three bones 

 of adults there is, as Dr. Doran says, no trace of such an aperture. 



S 3 



