MAMMALIA. EDENTATA. 351 



Subclass III. MONODELPHIA OR EUTHERIA. 



This great group includes all the Mammalia except the 

 orders Monotremata and Marsupialia. Coming to their 

 general characteristics as in the Didelphia the odontoid 

 process and cervical ribs early become fused with the centra 

 which bear them, while the coracoid is reduced so as to form a 

 mere process on the scapula, and there is no precoracoid (epi- 

 coracoid), such as is found in Ornithodelphia. Clavicles may 

 be present or absent ; when fully developed they articulate 

 with the sternum, usually directly, but occasionally, as in some 

 Rodents and Insectivores, through the remains of the sternal 

 end of the precoracoid. There is never any interclavicle in 

 the adult, though sometimes traces of it occur during develop- 

 ment. In the pelvis the acetahula are imperforatc ; and well- 

 developed epipubic bones are never found in the adult, 

 though traces of them occur in some Carnivores and foetal 

 Ungulates. 



Order 1. EDENTATA '. 



Teeth are not, as the name of the order seems to imply, 

 always wanting; and sometimes they are very numerous. 

 They are, however, always imperfect, and, with very few 

 exceptions, are homodont and monophyodont. They have 

 persistent pulps, and so grow indefinitely and are never rooted. 

 In all living forms they are without enamel, consisting merely 

 of dentine and cement, and are never found in the front part of 

 the mouth in the situation occupied by the incisors of other 

 mammals. These characters derived from the teeth are the 

 only ones common to the various members of the order, 



1 See W. H. Flower, "On the Mutual Affinities of the Animals com- 

 posing the order Edentata," P. Z. S. 1882, p. 358. For the fossil 

 Edentates of N. America see E. Cope, Amer. Natural. 1889; for those of 

 S. America see various papers by F. Ameghino, H. Burmeister and E. 

 Owen. Also T. H. Huxley, "On the Osteology of Glyptodon," Phil. 

 Trans. 1865. 



