408 MR. A. H. G. DORAN ON THE MORPHOLOGY 



maximus, PL LX. fig. 6). The head of the malleus of that animal is large, rising well 

 above the articular surface, but much flattened, laterally. The articular area is deeply 

 cut ; each facet has a vertical ridge running down the middle, meeting its fellow at the 

 groove of separation. Of the two segments thus formed in each facet the outer are most 

 concave, the inner almost fiat. There is absolutely no neck ; and the manubrium runs 

 almost in the axis of the body, and springs from close under the lower border of the arti- 

 cular surface. This process in S. maximus is narrow throughout, but flattened laterally, 

 and terminates in a well-developed disk. Halfway down its inner border is a slight 

 projection ; this is the processus muscularis (PL LX. fig. 6,pm), — very frequently in that 

 position among Rodents. The processus gracilis, which I have found entire in a large 

 adult skull, is very long, thin, and straight ; and a small area of friable opaque bone 

 extends from the head to its root. The incus has a moderately developed body, a short, 

 pointed, and non-divergent posterior crus ; and the processus longus is broad at the root 

 vertically, long, very straight, and widely divergent; it turns up very sharply at the 

 extremity, which is tipped by a minute elliptical Sylvian apophysis. The stapes is 

 large, with extremely slender crura ; the anterior is the thinnest ; both are slightly curved 

 and very divergent. There was no bony canal between the crura in the skull whence 

 the stapes was extracted for the College collection ; but an intercrural canal was found in 

 S. vulgaris, S. bicolor, and'iS'. carolinensis. The base is thin and slightly bullate towards 

 the vestibule; its extremities, especially the anterior, extend considerably beyond the 

 attachment of the crura. 



In the Jelerang Squirrel (S. bicolor) the ossicula are very similar, but the termination 

 of the manubrium is spatulate rather than discoidal. This process, moreover, is broader 

 at the root ; and the processus muscularis, on the inner border, is very prominent. In 

 the Common Squirrel (S. vulgaris) the manubrium mallei is even broader, but the 

 termination is an almost perfect disk. The processus muscularis is in the same position 

 as in S. maximus. In a young British Squirrel's skull I found the processus gracilis 

 of the malleus nearly five millimetres in length, running free for two fifths of its length 

 from the ossicle, beyond which it becomes a little dilated, and is fused by its inner border 

 to the neighbouring bone ; its extremity is a little rounded. 



In Tamias striatus (PL LX. fig. 9) the malleus resembles closely that of 8. vulgaris in 

 every respect, especially in the manubrium ; but at the point where that process leaves 

 the body of the ossicle there is a blunt angular projection, a rudimentary processus brevis 

 The body of the incus is very shallow. The stapes has a bony canal between its 

 crura *. 



In the European Souslik (Spermophilus citillus, PL LX. fig. 10) the malleus, in general 

 respects like that ossicle in Sciurus vulgaris, has a still more distinct trace of a processus 

 brevis (pb) than has Tamias. The incus is of the Tamias form; and there is a bony 

 canal between the crura of the stapes. 



The malleus of Anomalurus fraseri (PL LX. fig. 8) is of about the same size as that of 

 Sciurus bicolpr ; the manubrium is broader and more flattened laterally than in the true 



* In the Bristly Ground Squirrel (Xerus setosus) the ossicula are very similar. 



