No. 443.] 



HABITS IN MAMMALS. 



735 



is perhaps the most important element in the arboreal limb. It 

 disappears however when the animal moves in suspension as in 

 the sloths. 



5- The clavicle and scapula are well developed. These give 

 strength to the fore extremities and thus increase the climbing 

 power. It is interesting to observe that, as occurs in the 1 Ivstrie- 

 idae, the clavicles will be developed in one arboreal form while a 

 terrestrial member of the same family will have vestigial clavicles 

 or none at all. Together these two bones strengthen the pec- 

 toral arch " in the transverse direction : that is, against lateral 

 strains of pulling and pushing, which came almost entirely from 

 trie use of the anterior limbs (Cope)." 



6. The ilium is broadened in some forms, particularly in 

 Anthropoidea and the tree sloths. This adaptation is for the 

 support of the viscera. In the edentates the pubis is directed 

 posteriorly. 



7- In arboreal forms the ribs and chest are powerfully 

 developed as compared with the conditions in their noiwirboreal 

 relatives. 



