460 MR. A. H. G. DORAN ON THE MORPHOLOGY 



this genus by a minute pit ; and in no specimen of any Dolphin of any age in the Col- 

 lege Museum was it found ankylosed to the petrous bone, nor in any otber Cetacean except 

 Balcena mysticetus, and then not invariably. Hyrtl, who has described the ossicula of 

 the Cetacea (op. cit.) far more extensively than any anatomist before him, states that all 

 trace of the aperture is effaced "in Delphinus longirostris, braziliensis, tursio and 

 rissoii ;" but he asserts that it is also absent in Monodon, though a distinct trace is seen 

 in the two College specimens from different skulls ; and although he finds that the 

 aperture " reappears in the Porpoise," it does not seem more distinctly indicated in the 

 examples in the College collection than in Delphinus, and is decidedly not pervious. 

 The distinguished anatomist continues : — " Possibly this depends on the age of the 

 individual specimen ; a conjecture, however, not justified by the persistence in all other 

 animals of the form of the stapes in different degrees of age." I have not found the 

 aperture more blocked up or less clearly indicated by a depression in adult than in 

 young Delphinoid crania ; and, on the other hand, a specimen of the stapes of Bradypus 

 tridactylus in the College collection, from an adult Sloth, has a much smaller aperture 

 than another stapes from a cranium of a younger animal of the same species. 



In Globiocephalus (PI. LXIII. figs. 4 & 15) the head of the malleus is rather larger 

 than in Delphinus, and the projecting tubercle rather smaller ; but it is marked at its 

 apex by a distinct rough surface for the insertion of the tensor tympani tendon (pm), 

 and the manubrium (run) is represented by a very sharp spine pointing backwards and 

 flattened against the inner side of the ossicle. The bony process connecting the malleus 

 to the tympanic bone is rather long, and the same elements as described in Balcena 

 may be observed in it ; the processus gracilis (pg) or the anterior column is thick. The 

 incus has the same characters as in Delphinus ; the stapes, too, is very similar, but some 

 specimens have a pervious aperture. 



In a Lagenorhynchus in the British Museum the ossicula are of the same form as in 

 the last genus, and the manubrium is as well developed (fig. 11). In Phoccena the 

 malleus (fig. 5) most resembles that of Globiocephalus ; the incus is very similar, and 

 the stapes has generally a very minute but pervious intercrural aperture. The malleus 

 is connected by bone to the tympanic, though by a somewhat thin processus gracilis, 

 contrary to Hunter's experience. 



In Delphinapterus albicans (PI. LXIII. fig. 8), the Beluga or "White Whale, the 

 malleus much more resembles that of Delphinus than the same ossicle in Globiocephalus, 

 the process in front of the head being rather long and curved outwards. The recurved 

 splinter representing the manubrium in other Dolphins is quite absent, and represented 

 by a rough ridge (mn), hardly visible except by aid of a lens *. There is no excavation 

 on the outer aspect of the head of the Dolphins as in Balcena ; it seems as if the edges 

 so prominent in the Greenland Whale had rolled in and filled up a cavity, and to a less 

 extent in Physeter. 



The incus of Delphinapterus is of the form prevailing among the Delphinidae. The 

 stapedes in the College collection have neither so much as a trace of an aperture. 



* As the malleus of this Dolphin is larger than that of most Globiocephali, the absence of the spine-like manu- 

 brium (as in the smallest Delphini) is not due to diminished proportions or development of the entire ossicle. 



