STRUCTURE OF THE VERTEBRATES 123 



Friction ridges are found on the soles and palms. These are 

 evidently remains of the scaly covering of the ancestral types. 

 Following the work of Galton the study of finger prints has be- 

 come an independent science. As no two hands entirely agree in 

 configuration, but fall into definite groups, indexing is easy and 

 identification is absolute. These ridges apparently change little 

 throughout life, and if all hospitals adopted the methods of the 

 more progressive ones in making finger or foot prints of the 

 mother and newborn child before leaving the operating room, 

 the too frequent litigations over mixed babies in hospitals would 

 end immediately. 



The sweat glands pass well into the dermis before coiling, and 

 are distributed over the entire body without relationship to the 

 hair follicles. The sebaceous glands, on the other hand, evidently 

 developed in correlation with hair. In the human these are quite 

 large. If the follicle of the hair is closed, the secretion continues 

 and the gland may hypertrophy. The result is a spherical mass 

 under the skin, the larger ones being called wens. 



Technically speaking there are no "pores" in the skin. The 

 only openings are the follicles and the sweat glands, and these 

 end blindly in the dermis. There is no possibility of a respiratory 

 function, although some excretion takes place. Therefore, the 

 alleged cases of individuals dying from sealing the pores were 

 caused by lead poisoning or other extraneous conditions. The 

 fallacy is kept alive by soap manufacturers and the mothers of 

 boys. 



Hair distribution has been mentioned in relation to the sex 

 differences and regional distribution. Related to the latter is pat- 

 tern distribution on the body. It is common observation that the 

 hair of the head grows away from the crown, and a secondary 

 crown or "cow^ lick" is not uncommon. The body hair has similar 

 patterns. In general terms, the direction of hair growth is the 

 same as the scale direction of the reptile: (1) from anterior to 

 posterior, and (2) from dorsal to ventral. On the human back 

 the pattern lines are antero-posterior along the spinal column, 

 but dorso-posterior on the sides. This is similar to the pattern 

 of the other primates. 



Embryologically hair arises in groups of three or four, again 

 indicating a scale pattern as found in ]\Ianis. During later em- 



