THE SKELETON IN MAMMALIA. AUDITORY OSSICLES. 487 



ossicles, the malleus much resembling that of many Insectivores, 

 and the stapes having two definite crura separated by a canal. 



In EDENTATES the character of the ossicles varies much. 

 In Sloths the stapes approaches that of Sauropsids in its 

 narrowness and the slight trace of a canal ; this character 

 is however still more marked in Manis, whose stapes is as 

 Sauropsidan as that of Monotremes, and consists of a nearly 

 circular basal plate bearing a column which does not show any 

 sign of division into crura. The stapes of other Edentates, 

 such as anteaters, aard varks, and most armadillos, is of a high 

 type and has well-developed crura. Priodon has a lower type 

 of stapes than Dasypus and Tatusia. 



The ossicles of the SIRENIA differ widely from those of all 

 other mammals in their great density and clumsy form. 



In CETACEA the ossicles are solid, though not so solid as in 

 Sirenia, and their details vary much. The malleus is always 

 firmly fused to the tympanic by means of the processus longus, 

 and the manubrium is very little if at all developed. The 

 incus has the stapedial end greatly developed, and the stapes 

 has very thick crura with hardly any canal. The ossicles of 

 the Mystacoceti are apparently less specialised than are those 

 of the Odontoceti. 



The auditory ossicles of the UNGULATA do not present any 

 characters common to all the members of the group. 



Among Ruminants they are chiefly remarkable for the 

 development of a broad lamellar expansion between the head 

 and the processus longus of the malleus. In some cases the 

 malleus of the foetus differs strikingly from that of the adult. 

 Among Perissodactyla the Rhinoceros and Tapir have the 

 malleus of a low type, recalling those of Marsupials ; while in 

 the Horse the head is well developed, and the malleus is of 

 a higher type. 



The ossicles of Procavia, which recall those of the Equidae, 

 are chiefly remarkable for the small size of the body of the 

 incus. In Elephants the ossicles are large and massive. 



