OF THE MAMMALIAN OSSICULA AUDITUS. 441 



the constriction appears all the greater on account of the narrowness of the lamina. 

 Close to the narrowest part, on its inner aspect, the neck hears a distinct, curved pro- 

 cessus muscularis. I can detect no trace of any orbicular apophysis. 



The manubrium is long and rather narrow at the base, which bears externally a trace 

 of a processus hrevis. Its outer aspect is not only sharply bordered from the sides, but 

 remarkably and almost uniformly broad; the extremity is but slightly dilated and 

 recurved. 



The lamina is extremely narrow, owing to the processus gracilis joining rapidly a 

 process from the head, and thus leaving little room for any area of lamellar bone. The 

 processus gracilis thus reinforced forms a thin straight bar of bone, which runs half 

 across the front of the tympanic cavity, to fit into the Glaserian fissure, quite different 

 from what prevails in the preceding families of the Insectivora, where that process runs 

 downwards at once, and is curved so as to fit accurately to the tympanic ring. 



The incus lies almost vertically above the malleus in the recent skull; it has a 

 well-developed square body ; the part above the processus longus overhangs that pro- 

 cess. The processus brevis is stout, blunt-pointed, and does not diverge from the body. 

 The stapedial crus is straight and freely divergent; it supports a very small Sylvian 

 apophysis. 



The stapes has an ill-developed body, and long, slender, extremely straight crura. The 

 aperture is wide and triangular, though not as wide as in the Shrews and Hedgehogs. 

 A very stout bony canal fills it during lifetime. The base is rather broad, and convex 

 towards the vestibule. 



The malleus of Bhynchocyon cimei (PI. LXII. fig. 16) resembles that of Macroscelides 

 in general characters, particularly in the narrow neck and singular processus gracilis ; 

 but the head is better-developed, and the processus muscularis is still stouter and more 

 curved. The incus is very like that of the Elephant-shrew ; its stapedial crus bears a 

 fairly developed Sylvian apophysis. The crura of the stapes are very slender. 



It is remarkable that in Petrodromus (fig. 19) (the ossicula of which I have been able 

 to examine through the kindness of Dr. Guuther) the malleus is much more Shrew-like 

 than in the Elephant-shrew. The lamina is wider ; and there is a trace of an' orbicular 

 apophysis. The processus muscularis and the manubrium are of the same form as in 

 Macroscelides. As for the incus of Petrodromus, it is not only quite unlike that of Sorex 

 or Erinaceus, but in its high and narrow body it diverges also from Macroscelides and 

 Bhynchocyon, and tends towards Tupaia. The stapes has straight crura, with a bony 

 canal between them in the recent skeleton. 



In Tupaia the malleus differs from that of any other insectivorous mammal (PI. LXII. 

 fig. 17). The head of the malleus is broad antero-posteriorly, but flattened laterally. It 

 supports a very shallow articular surface, saddle-shaped, and only indistinctly divided 

 into two facets. There is not a trace of any neck or lamina ; the tensor-tympani tendon 

 is inserted into the root of the manubrium. This latter process arises from the head 

 directly, and has no angle at the outer side of its base corresponding to the processus 

 brevis. It is not very broad at the base, and is very little dilated at the tip ; its outer 

 aspect is distinctly bordered from the sides. 



