330 THE ANATOMY OF VEETEBRATED ANIMALS. 



and lieterogeneous assemblage called Edentata. Some of 

 the members of this group certainly possess deciduate pla- 

 centae, while, in others, it appears questionable whether 

 the decidua is, or is not, developed. And as this group, 

 the Edentata, is decidedly the lowest of the whole division, I 

 shall take it first in order, while the Sirenia are arranged, 

 provisionally, among the Non-deciduata. 



The Edentata, or Brttta. — In these Mammals the 

 teeth are by no means always wanting, as the name of the 

 group wotdd seem to imply ; but, when teeth are present, 

 incisors are either altogether absent, or, at any rate, the 

 median incisors are wanting in both jaws. The teeth are 

 always devoid of enamel, consisting merely of dentine and 

 cement. As they grow for an indefinite period they never 

 form roots; and, so far as our knowledge at present 

 extends, those which first appear are displaced by a 

 second set only in some of the Armadillos. The ungual 

 phalanges of the digits support long and strong claws. 



There are mammse upon the thorax, and sometimes, in 

 addition, on the integument of the abdomen ; or, in the 

 inguinal region. 



The brain varies gi'eatly, its hemispheres being some- 

 times quite smooth, with a very small corpus caUosxim and 

 large anterior commissiire ; while, in other cases, the cor- 

 pus callosum is much larger, and convolutions appear upon 

 the sarface of the brain. 



The Edentata are divided into the Phytophaga, or vege- 

 table feeders, and the Entomophaga, or insect-eating forms. 

 Leaves are the chief food of the former group, while the 

 latter delight chiefly in ants, though some take, in addition, 

 worms and carrion. 



1. In the Phytopliaga the long bones are without me- 

 dullary cavities. The lateral iDart of the zygomatic arch 

 sends down a remarkable vertical process. The acromial 

 process of the scapula coalesces with the coracoid. In the 

 carpus, the scaphoid and the trapezia! bones ankylose and 

 form one. The ischia become united with the anterior 



