THE STRUCTURE OF THE VERTEBRATES 341 



g. Anterior limbs become wings ; surface covered 

 with feathers ; teeth lost in modern forms. (Birds.) 

 From these nothing further arises. 



h. Covering of hair ; in higher forms young nourished 

 in body of parent. (Mammals.) 



i. Upright posture, with freedom of anterior feet as 

 hands to make tools ; corresponding development of the 

 brain to guide the work. (Man.) 



References 



HUXLEY, T. H. Manual of the Anatomy of Fertebrated Animals. D. C. Ap- 

 pleton Company, New York. 



KELLICOTT, W. E. Outlines of Chordate Development. Henry Holt & Co., 

 New York, 1913. (Embryology of vertebrates.) 



PRATT, H. S. A Course in Vertebrate Zoology. Ginn & Co., Boston, 1905. 

 (Anatomy of selected types.) 



JORDAN, D. S. Manual of the Vertebrate Animals of the Northern United 

 States. A. C. McClurg & Co., Chicago. Eighth Edition, 1899. (Clas- 

 sification, with descriptions of the genera and species. The region 

 covered extends west to the Missouri River.) 



GREGORY, W. K. Present Status of the Problem of the Origin of the Tetra-poda 

 (four-footed animals). Ann. N. Y. Acad. Sci., XXVI, 1915. 



