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



slender, and not very divergent near the base. There is a bony canal between them in 

 the recent skull. 



In the Hamster ( Cricetus frumentarius) the malleus has nearly as well-developed a 

 lamina as in Mus ; there is no orbicular apophysis ; and the manubrium is not so broad 

 at the base as in the other Muridse. The processus brevis of the incus is very ill- 

 developed, a character more pronounced in Castor and Fiber than in Mus. There is a 

 bony canal between the crura of the stapes. 



As an example of the Siphneinse, the malleus of Mlobius talpinus is somewhat rat-like 

 in form, having a small head and a distinct lamina ; the manubrium bears a processus 

 brevis close to its root. It is sometimes partially ankylosed to the incus. The incus 

 itself has a very ill-developed body with well-developed crura, a feature seen in the 

 fossorial rodent families distinct from the Muridse, and about to be considered. The pro- 

 cessus longus is much longer than the posterior crus. The stapes has very slender crura, 

 between which runs a very dense bony canal in the recent skeleton. 



Coming to the Spalacid^e, considerable variety will be found in the ossicula of pro- 

 minent genera. In Spalax typhlus (PI. LX. fig. 19) the head of the malleus is ill- 

 developed and laterally flattened, with a very shallow articular surface, hardly any trace 

 of a lamina, and a very constricted neck. The manubrium runs almost in the axis of the 

 neck ; it is short, and is very broad at the base, much laterally compressed ; there is a 

 prominent angle representing the processus brevis. In its malleus Spalax bears the 

 same relation to Geomys that Castor does to Arctomys, the mallei in Geomys and 

 Arctomys being quite neckless ; otherwise, in the flattened heads, with wide and shallow 

 articular surfaces, they all bear a certain relation to one another ; and all seem inter- 

 mediate between Sciurus and Mus. 



The incus of Spalax much resembles that of Mlobius; but the body and articular 

 surface are still shallower * ; the crura are very similar in form and proportion. The 

 stapes is of an extraordinary and quite unique type. It is very large, measuring from 

 head to base two millimetres, the base of the skull measuring from the prsemaxilla to the 

 occipital foramen not quite five centimetres, whilst in a skull of Capromys, measuring 

 over eight centimetres, the stapes is only a millimetre and a quarter in height. The 

 head is a small narrow rod ; the anterior crus is very straight, and runs forward at a great 

 an^le to the posterior, which is much bowed, and inserted into the corresponding 

 extremity of the base almost vertically under its origin. The base is well developed, 

 convex, both vertically and horizontally, and very reniform, its lower border being con- 

 cave. There is no bony intercrural canal in the recent skull. 



In the Bay Bamboo Rat (Rhizomys badius, PL LX. fig. 20) the head of the malleus is 

 well developed and not much compressed laterally : the articular surface is much deeper 

 than in Spalax or Mlobius ; and the neck is long and constricted. There is a trace of 

 a lamina ; and the head is prolonged into a point forwards as in Fiber ; near the root 

 of the manubrium is a small tubercular processus muscularis. The manubrium is longer 

 than in Spalax, and forms a sharper angle with the neck ; it is of similar shape, and 

 very broad laterally. The malleus of Rhizomys bears a strong resemblance to that of 



* The posterior part of the body is much deeper than the anterior. 



