108 On the Auditory Ossicles of the Mammalia. [June 15^ 



shallow, with an even, stouter, and more divergent posterior crus than 

 in other ruminants. The stapes remains triangular in full-grown large 

 deer. Moschus is quite cervine in its ossicula, the shallow body and 

 thick, long, divergent posterior crus of the incus being very different 

 from the square-bodied incus with short crura seen in the Tragulidse. 



Among the E-odejn^tia we find great variety in the form of the auditory 

 ossicula in different families, as is also the case among the Insectivora. 

 Nearly every type of malleus may be observed among the various sub- 

 divisions of the order, such as the large-headed, distinctly necked form 

 of the higher Primates, the neckless variety of the lower monkeys, the 

 laminated type of the ruminants and terrestrial carnivora, and the fused 

 condition of the malleus and incus of the guinea-pig and its allies. The 

 stapes, too, varies, being sometimes large in proportion to the size of the 

 animal, in other cases very small in large species. 



The most constant character in the rodent's malleus is the broad, 

 laterally tlattened manubrium, with a processus muscularis on its inner 

 edge far from the neck of the ossicle, which may be said to present three 

 prevailing types — the neckless form in the squirrels, the lamina,ted 

 variety of the rats, and the malleo-incudal fusion of the Hystricidse. 

 The incus varies little, and its processus brevis is always shorter than 

 the anterior crus, and but little divergent. A bony canal between the 

 crura of the stapes is frequent in several families. 



Classifying the animals intermediate in the character of the malleus 

 between the genus Sciurus, where it is neckless without a trace of any 

 processus brevis, and Castor, where both neck and process exist, the genera 

 will be found to run as nearly as possible in the following order : — 

 Sciurus, Anomalurus, Marmotta, Tamias and S'permoijhilus, Pteromys, 

 Myoxus and Castor, the separation of the head from the manubrium 

 becoming more and more apparent in each of these genera towards the 

 last ; but, taking other points into consideration, Anomalurus should be 

 placed after the ground-squirrels, having a small stapes with crura not 

 very divergent, as in the Hystricidae ; and Mannotta separates itself from 

 other sciuroid rodents by the peculiar form of its head, which is ex- 

 tremely flattened laterally and projects above the articular surface. In 

 all the above rodents, except Anomalurus, the stapes is large, with wide, 

 thin, divergent crura ; and an intercrural bony canal exists in most 

 species. 



In the Muridse the malleus has a well-formed lamina and a manubrium 

 rather broad at the base. The former peculiarity is most marked in 

 Mus, Haixilotis, Hydromys, and their allies, where an orbicular process 

 standing out from the front of the neck is a frequent feature, and appears 

 identical with a similar projection in the shrews, and is probably an 

 extreme development of the sharp angular protuberance seen in the 

 malleus of the badger, and in that from a Bassaris in the College col- 

 lection. In Fiber the lamina is smaller and the manubrium broader than 



