OF THE MAMMALIAN OSSICULA AUDITUS. 459 



than in that Whale, nor is the upper much larger than the lower. The processus mus- 

 cularis is a short blunt point. I found a few shreds of the tendon of the tensor tympani 

 adherent to it. The manubrium is represented by the faintest trace of a tubercle ; there 

 is a ridge above it, into which a part of the process from the membrana tympani is pro- 

 bably inserted as in Platanista. 



The processus gracilis and its accessories connecting the malleus to the tympanic bone 

 is extremely short, and the depression in the head above it almost effaced. See PL LXIII. 

 figs. 19 & 19 a, where this bone in the closely allied Mesoplodon grayii is shown. 



The incus is of the same character as in Hyveroodon and Berardius ; it is rather 

 smaller in proportion to the malleus. The ridge separating its facets is almost as sharp 

 as in Hyperoodon. 



Taken as a whole, and judging from the incus as well as the malleus, Mesoplodon 

 resembles Hyperoodon rather than Berardius. In the ill-development of the head of the 

 malleus we have a character which should place this Whale between Physeter and 

 Hyperoodon. In the smallness of the articular surface of the malleus it differs alike from 

 the Cachalot and Berardius, and approaches Hyperoodon. 



The stapes has no aperture, and in form coincides with the same ossicle in. Hyperoodon, 

 confirming the remarks in the last paragraph. 



In the Delphinidae the ossicles may be said to be central in character among the 

 Cetacea, the Balsenoidea and Platanistidse departing from them towards other mammals, 

 the Physeteridse diverging, on the other hand, from the Dolphins in the highly specialized 

 characters of the malleus and incus. It is remarkable that among the Whales proper 

 the genus Balcenoptera should so closely resemble the Dolphins in its ossicula. 



In Delphinus the malleus (PI. LXIII. figs. 2 & 3) in general form reminds the observer 

 strongly of the same in Balcenoptera*. The outer aspect of the head is less flattened, 

 the articular facets are similar, the upper being the larger and planer, the lower the most 

 convex; but instead of the large rounded tubercle seen in the Whale just mentioned, a 

 small, blunt, slightly excurved process projects from the head in Delphinus. On its 

 inner surface may be observed a small spine (mn), directed backwards, hardly perceptible 

 to the eye, yet readily detected by rubbing the finger forward over the internal aspect of 

 the malleus. This represents the very perceptible homologue of the manubrium 

 described as existing in the Pike- Whale, and equally or more developed in other genera 

 of Dolphins f. 



The body of the incus is very feebly developed, being, as it were, absorbed by the 

 stapedial crus. Its articular surface has facets divided by a sharp ridge, as in the 

 Balsenoidea, and unlike Physeter and Berardius. The processus brevis is very slender 

 and much shorter than in the Ziphioids ; the processus longus is very stout, and shaped 

 like its representative in Balcenoptera ; the Sylvian apophysis is of the same nature. 



The stapes is about a line in length, with fairly divergent crura and a very thick base, 

 quite concave towards the vestibule. The aperture is closed, but always represented in 



* The ossicula of a foetal Dolphin, four inches in length, are all of precisely the same form as in the adult, 

 t the homologous parts of the malleus in the Dolphins are indicated in PI. LXIII. fig. 15, representing that 

 ossicle in Globiocejphaliis (see also figs. 3 to 12). 



