462 MR. A. H. G. DORA.N ON THE MORPHOLOGY 



thicker stapedial eras than in other Delphinoidea * ; the posterior is short and small ; and 

 the facets are, of necessity, of equal size ; they are divided by a sharp and prominent ridge. 

 The stapes is of the ordinary Dolphin type, with a very thick base, generally (but not 

 always) very concave towards the vestibule. It was found unankylosed to the fenestra 

 ovalis in a large adult skull in the College Museum. The ossicle in this case had a 

 minute almost pervious depression between the crura. 



In the ossicula of the Platanistid^: we find interesting modifications. In the Gangetic 

 Dolphin (Platanista gangetica) the head of the malleus (PL LXIII. figs. 12 & 17) is 

 of the same form as in Delphinus, and the upper facet is larger than the lower ; but the 

 process in front is extremely elongated, so as to be longer than the head itself, from 

 which it is hardly more distinct than in Monodon, except that a faint groove, generally 

 observed in the true Dolphins, divides them above and internally. Instead of a rough 

 and only slightly concave surface at the very extremity of the process, as is found in 

 most Cetacea to mark the insertion of the tensor tympani, there is a very deep pit on 

 the external aspect of the projection, actually nearer its root than its point ; this is 

 highly characteristic (fig. 17). The point itself is sometimes slightly hooked ; and 

 from it to close under the articular surface, all along the inner aspect of the process, 

 runs a very distinct groove, ending posteriorly in a faintly marked tubercle representing 

 the manubrium (fig. 12, mn) It seems as if the groove were homologous with 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 macerated specimens. In Monodon and the 

 Dolphins proper some of the fibres are in the same manner inserted along the back of the 

 anterior projection from the head of the malleus, as well as to the splinter-like more 

 definite homologue of the manubrium f . 



The processus longus of the incus (fig. 20) 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 intercrural aperture ; there is sometimes a large tubercle for the stapedius- 

 tendon on the inner aspect of the head. 



By the kind permission of Dr. Giinther I have been enabled to examine the ossicula 

 from the skull of Inia geoffroyii belonging to the British Museum. The general shape 

 of the malleus (PL LXIII. fig. 10) reminds the observer more of Delphinus than Pla- 

 tanista. The head and facets resemble the same in the Gangetic Dolphin ; but the process 

 in front is not nearly so produced as in Platanista. The tensor tympani is inserted into 

 ■ a pit (at pm) as in the Gangetic genus, which, however, is seated in Inia quite at the 

 tip of the process from the malleus, on the site of the same insertion in Delphinus. The 

 manubrium is a very distinct reflected spine (mn) ; and there is a groove running 



* Hyrtl (op. eit.) directs attention to the small size of the articular surface for the head of the stapes on the end ot 

 this process. 



t In making a fresh dissection of the tympanum of Platanista, I found a strong band of fibres inserted into the 

 groove, and the tensor tympani was inserted into the depression above described (PI. LXIII. fig. 17). 



