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 Vertebrated 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 Tetrapoda 

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



