THE SKELETON IN MAMMALIA. THE SKULL. 459 



the ptery golds meeting in the middle line just like the pala- 

 tines. The mandible is very long and slender, there being no 

 definite coronoid process, and a short and slight symphysis. 

 The hyoid arch is noticeable for the length of the anterior 

 cornu. 



In the Armadillos (Dasypodidae) the skull varies a good 

 deal in shape, but the facial portion is always tapering and 

 depressed. The zygomatic arch is complete. In Dasypus and 

 Chlamydophorus the tympanic bulla is well ossified. 



In the Glyptodontidae the skull is very short and deep ; 

 the zygomatic arch is complete, and has a long downwardly 

 projecting maxillary process. The mandible is massive, and 

 has a very high ascending portion. 



In the Manidae the skull is smooth and rounded, the zygo- 

 matic arch is incomplete, and the orbit is inconspicuous. The 

 palate is long and narrow, but the pterygoids do not take part 

 in its formation. The mandible is slightly developed and has 

 no angle or coronoid process. 



In Orycteropus the zygomatic arch is complete, and there 

 is a small postorbital process to the frontal. The mandible is 

 well-developed, having a coronoid process and definite ascending 

 portion, and the hyoid is well ossified. 



SIRENIA. The skull, and especially the brain case of all 

 Sirenia, is remarkable for the general density of the component 

 bones, which, though often very thick, are without air sinuses. 

 It is noticeable also for the roughness of the bones, and the 

 irregular manner in which they are united together. 



The cranial cavity is decidedly small, the reduction being 

 specially noticeable in the cerebral fossa, which is not much 

 larger than the cerebellar fossa. The foramen magnum is 

 large, and the dorsal surface of the cranium narrow. The 

 zygomatic arch is very strongly developed, the squamosal (fig. 

 92, 4) being especially prominent, and being drawn-out not only 

 into the zygomatic process, but also into a large post- tympanic 

 process which articulates with the exoccipital. At the side 



