OF THE MAMMALIAN OSSICULA AUDITUS. 465 



so as to be often invisible from tbe external meatus ; tbe processus gracilis stretches well 

 forwards from tbe rest of tbe malleus ; and tbe articular surface is placed almost wholly pos- 

 terior. In tbe Cetacea, on the other hand, the head of the malleus is much less posterior in 

 position, the processus gracilis runs from it directly outwards to join the tympanic bone, 

 and the facets look inwards. In the Dugong and Manatee the malleus holds an inter- 

 mediate position, as may be seen by examining a skull of Halicore in tbe College 

 Museum (No. 2633), where all the left ossicula are in situ. The head lies quite anterior 

 to the posterior horn of the dense annulus tympanicus, its manubrium projecting directly 

 outwards from it ; the processus gracilis runs as completely forwards as in terrestrial 

 mammalia ; but, again, the articular surface is as internal as in the Whales and 

 Dolphins. 



The massive head of the malleus of Halicore amtralis is of irregular shape, about as 

 long antero-posteriorly as vertically, and slightly flattened from within outwards. Its 

 uppermost portion is wide, slightly convex, and does not project above tbe upper facet 

 as in most Mammals. The articular region lies entirely on the very broad inner aspect 

 of the ossicle. It is made up of an upper facet and two lower, which latter represent 

 the single inferior facet in other mammals, the extero-inferior segment of the articular 

 surface of the human malleus ; they form almost a right angle with each other, and an 

 obtuse angle with the upper facet, a very distinct groove dividing them. The superior 

 facet is reniform, with its long axis vertical, and its concavity forward ; its surface is 

 distinctly convex from above downwards. Tbe smaller inferior facets * are oval ; and 

 their edges generally coalesce along the high ridge which divides them, and whence 

 they slope. On the outer aspect of the malleus is a very deep groove running forwards 

 and slightly downwards ; its upper border is thick and prominent ; its lower is formed by 

 tbe root of tbe manubrium. This projecting upper border is homologous with the sigmoid 

 ridge on the neck of the human malleus, as may be seen by laying an ossicle of Homo 

 and of Halicore side by side, with the manubrium forwards. Hence it must represent 

 tbe sobd curved neck of tbe laminar type of malleus in the Carnivora, Ruminants, and 

 other Mammals f. Completely in front of the malleus of the Dugong is the processus 

 gracilis (PI. LXIII. figs. 26, 27), which is broad at its root, but narrows rapidly. 

 Owing to the whole ossicle being placed unusually forwards this process is far shorter 

 than in terrestrial Mammals. Its upper surface is smooth and convex, being con- 

 tinued from the upper surface of the head ; its lower is flat and very short, separated 

 by a deep horizontal groove from a prominent tubercle on the front of the head below 

 it. The processus muscularis is a blunt tubercle, looking forwards from the inner 

 aspect of tbe malleus, and is continued backwards and upwards as a very promi- 

 nent convex ridge, which is lost on the head of the malleus behind the inferior facets, 

 near the ridge on the anterior aspect already described. Strictly speaking, the whole 

 must be considered as the processus muscularis, having its root on the true neck (the 



* These evidently represent the inferior facet of other animals, the convex ridge being here much exaggerated, 

 even to the point of dividing that facet into two. 

 t See the account of the human malleus, antea. 



