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



The head is less developed than in Balcena, especially below and internally * ; it has a 

 deep depression externally, of which the borders are elevated, but not nearly so over- 

 hanging as in the Greenland Whale. The articular surface is very similar, and the 

 upper facet is the larger. In front of the head is a very prominent well-rounded tubercle, 

 on the under and inner surface of which is a sharp splinter of bone {mn), with its point 

 directed backwards ; it lies flat against the malleus. 



Hyrtl, in denying Cuvier's assertion that the manubrium is absent in Dolphins and 

 Whales, continues : — " It is only very short, and reduced to a rounded bony tubercle, 

 separated by a deep incision from the head." But in describing the tympanum of Mo- 

 nodon he remarks : — " The fleshy process of the membrana tympani is half an inch long, 

 and attached to a ledge [Leiste] on the outer border of the malleus." Now the malleus 

 of Balcenoptera is very similar to that of Monodon, and still more to that of Delphinus 

 and Bhoccena. By carefully dissecting the tympanum of a Monodon, and examining the 

 preparations of that cavity from all the remaining above-mentioned genera as seen in 

 the College Museum (Nos. 1590-3 and 1596), I find that the tensor tympani tendon is 

 almost invariably inserted into the most prominent and anterior part of the rounded 

 tubercle of the malleus, whilst the process from the membrana tympani f is inserted, as 

 Hyrtl says, into the splinter of bone described above ; it is, however, on the under, not 

 the outer surface of the malleus. Hence it must be correct to consider the bony splinter, 

 Hyrtl's " Leiste," as the manubrium, whilst the bony tubercle % should be considered 

 the homologue of the processus muscularis of other mammals. The short curved process 

 in the Greenland Whale, well divergent from the body, is evidently an intermediate 

 condition between the long manubrium of terrestrial quadrupeds and the flattened 

 splinter of Balcenoptera and the Dolphins. 



The process joining the malleus to the tympanic bone is very similar to that in 

 Balcena, but shorter. The anterior pillar, or true processus gracilis, is very stout, and 

 the lamina is rather denser than in Balcena. 



The incus (PL LXII. fig. 31) assumes, like the malleus, the form prevailing in genera 

 presently to be referred to. The body (which bears an articular surface similar to that 

 of Balcena) is very ill developed, and the posterior crus is almost atrophied ; it measures 

 about a line in length, though tolerably stout. The processus longus is enormously 

 developed, and incurved so abruptly as to present anteriorly a knee-like projection. On 

 its broad extremity it bears a smaller and narrower, thick and elliptical Sylvian apo- 

 physis, of about the size and shape of the base of a Squirrel's stapes. Hence the incus 

 of Balcenoptera differs from that of Balcena more than the latter is different from that 

 of most terrestrial Mammalia. 



The stapes (PI. LXII. fig. 31) is not so long as in the Greenland Whale, though its 

 crura are longer than in the Dolphins. The head is well developed, and bears a rough 



* It is much flattened on its outer and inner aspects. 



t See PI. LXIII. fig. 16, where the tendon of the tensor tympani and the process from the membrana tympani 

 (in Monodon) aro both indicated. 



% The exact site of the insertion of this tendon is marked by a rough surface in Balcenoptera, Orca, and most 

 other Cetaceans. 



