OF THE MAMMALIAN OSSICULA AUDITUS. 403 



latter peculiarity, also seen in Stenorhynchus, distinguishes the incus of Macrorhinus 

 from that of Phoca and Cystophora. The processus hrevis is a short process, very stout 

 at the base and blunt at the tip ; it does not diverge from the body ; the long crus is 

 short compared with the dimensions of the whole incus, rather thin, quite cylindrical, and 

 stretches well forwards from the body, with a wide curve, as in the Bears, the Sea-lions, 

 and the Walrus. This bone is only a caricature, so to speak, of the same condition seen 

 in Phoca (compare fig. 23, with fig. 27, PL LIX.) ; but whilst the posterior part of 

 the incus of Macrorhinus assumes and exaggerates the Phocine type, the long crus is, 

 as just noticed, rather like the same in the last families, Otariida? and Trichechidse ; 

 so that the incus of Macrorhinus is a truly central form. 



The stapes strongly resembles that of Trichechus, only it is of much stouter build ; the 

 head is even smaller ; the crura widen close below it, and then slowly approximate to the 

 base ; they are entirely fused ; but on the front aspect of the bone is a deep concavity, 

 representing the normal aperture. The base is a thick bordered facet, and is quite saddle- 

 shaped, being very convex vertically, though nearly plane horizontally. 



In Cystophora cristata (PI. LIX. fig. 25) the head of the malleus is flattened antero- 

 posteriorly, and somewhat oval, being broadest horizontally ; there is a concavity in 

 front and a facet behind, convex laterally and concave vertically, as in Phoca and 

 Macrorhinus, &c; but it occupies nearly the whole of the posterior aspect, being far 

 wider than in the latter, while the whole head is smaller. The neck is extremely long, 

 more so than in any other Seal, and almost perfectly cylindrical, being but little con- 

 stricted near the handle; it is, moreover, very straight. The manubrium is short, 

 rather narrow at the base, well recurved and dilated at the extremity ; it forms a very 

 obtuse angle with the neck, and bears a prominent blunt processus brevis. Altogether 

 this bone resembles the malleus of Phoca, from which it may at once be known by the 

 length of its neck. 



The posterior part of the body of the incus is well developed, and bulges internally, 

 but not nearly to the extent seen either in Stenorhynchus or Macrorhinus. There is a 

 shallow groove round the inner side of its facets, as seen in a more developed form in 

 Phoca. The processus brevis is short and stumpy; the longer crus is shorter and 

 stouter than in Macrorhinus; still it stretches well forward, and in that process 

 alone the incus of this animal resembles that of the last-described species rather than 

 Phoca. 



The stapes has an ill-developed head and very thick crura, both croo§ed. but the 

 anterior more so than the posterior. There is a considerable round aperture between 

 them ; the base is broader than in the last family, and slightly concave. 



This stapes is truly intermediate between that of the Pinnipedia already noticed and 

 those to follow. It differs from the former in having an intercrural space and a wider 

 base, and from the latter in that the space between the crura is very much more limited, 

 and, the crura being almost parallel, the base is therefore narrower. 



In the Stenorhynchina (see PI. LIX. fig. 26, Lobodon carcinophaga*), the head of the 



* SSyn. Stenorhynchus serridens, Owen, P.Z.S. 1843, p. 131, & Cat. Ost. Mus. Coll. Surg ii. p. 641. 



