OF THE MAMMALIAN OSSICULA AUDITUS. 413 



some of the less-typical Muridse, especially Fiber. The ossicle is decidedly not so 

 specialized as that of Spalax. The incus has a very shallow hody ; the posterior crus is 

 less developed than in the other genera, though the processus longus is stout and long 

 — a murine character. The stapes has straight crura, more divergent than in the Muridse, 

 and a very broad base ; there is no canal between the crura in lifetime. 



In the subfamily Bathyerginse the genus Bathyergus exhibits in its ossicles a feature as 

 distinctly allying it to the Cavies and Porcupines as the past fossorial rodents are allied 

 by other peculiarities to the Muridse, and more distantly to the Sciuridse. 



The head of the malleus (PL LX. fig. 22) is much elongated anteriorly, but not so 

 much as in the Hystricidae. The neck is thin and constricted ; and there is a distinct 

 laminar expansion beneath it. The manubrium is rather short ; it is tolerably wide near 

 the base, but gets very narrow towards the tip, and has a distinct processus brevis, and a 

 small stout tubercle on its inner border, representing the processus muscularis, as in many 

 Squirrels. The head of the malleus is completely fused to the body of the incus by their 

 articular surfaces, the contour of which is deeply marked all round the seat of ankylosis ; 

 the bony union involves the neck and a part of the inner border of the manubrium, 

 from the root to close above the tubercle for the tendon of the tensor tympani, the manu- 

 brium being fused to the processus longus of the incus nearly down to the point where 

 it turns inwards towards the head of the stapes. This ankylosis was observed by Hyrtl. 

 Whilst the malleus differs from the hystricine malleus in the head being less produced 

 forwards, the incus is distinguished from that of the Porcupines in having the very 

 shallow body and proportionally large crura seen in the rest of these fossorial animals. 

 The posterior crus is particularly long. The processus brevis is as well developed as in 

 Spalax or Ellobius, and hence different from the same in Bhizomys. 



The stapes (PL LX. fig. 22) is a large bone, though not proportionally as great as in 

 Spalax. Both crura are straight, not very long, and widely divergent. The base is very 

 broad, and extremely convex towards the vestibule ; the crura are inserted some distance 

 from both extremities. There does not appear to be any bony canal between the crura ; 

 at least such does not exist in the skulls of Bathyergus in the College collection. 



Among the Saccomtidje, in the Pouched Gopher (Geomys bursarius, PL LX. fig. 21) 

 the malleus is much flattened laterally, and the articular surface is extremely shallow, 

 long vertically and narrow in horizontal measurement ; there is no lamina, no trace of a 

 neck ; and the manubrium, which runs almost in the long axis of the head, is little com- 

 pressed laterally, and has no processus brevis. It more resembles the malleus of a 

 Beaver or Marmot than the same in Sciurus or Mus. 



The incus is of singular form; its body is extremely shallow; so is the articular 

 surface; the processus brevis is very stout and blunt, and disproportionately large, 

 whilst the anterior crus is very slender throughout, bearing a well-developed pedun- 

 culated Sylvian apophysis at its extremity. The stapes has rather stout well-diverging 

 crura ; the aperture is occupied, in the recent skull, by a very delicate ossified canal for an 

 artery. On its base there projects towards the vestibule a very large bulla, better 

 developed than in Mustela or Hyrax, and rivalling the same condition already described 

 by Hyrtl as existing in JPhakmgista cookii, 



SECOND SERIES. — ZOOLOGY, VOL. I. 3 K 



