6oo 



EDENTATES 



xxii. 6- 



The limbs are long, especially the fore-limbs, and the digits carry 

 hooked claws for hanging (Fig. 380). In the pectoral girdle the clavicle 

 articulates with the coracoid, a unique condition among mammals. As 

 in ant-eaters the acromion is connected with the coracoid, enclosing a 

 coraco-scapular foramen. The significance of these special features is 

 not clear, but the habit of hanging upside down has produced some 

 obvious modifications, for instance all the vertebral neural spines are 



Fig. 380. Skeleton of three-toed sloth, Bradypus. (After Blainville.) 



low and the pelvis is short. Even here, however, we find peculiar 

 similarities to the ant-eaters, in the union of the ischium with caudal 

 vertebrae, a feature whose adaptive significance is obscure. 



The sloths live on foliage, but this herbivorous diet is perhaps 

 secondary to a long period of insectivorous life, during which there 

 was a reduction of the teeth and loss of enamel. On adoption of the 

 new way of life the enamel could not be restored, but a grinding surface 

 is provided by the presence of cement and continuous growth of the 

 teeth. The stomach is large and divided into several chambers, recall- 

 ing those of ruminants. The rectum is enormous and the masses of 

 faeces are retained for several days, intestinal peristalsis being as slow 

 as all the other movements of these creatures. Interesting features con- 

 nected with this slow life are the small size of the thyroid and adrenals. 



The sloths live in the rain forests of South and Central America, 



