INTEGUMENTARY SYSTEM 105 



Hence, pigment is present in the skin, both in basement mem- 

 brane and corium, of men of all races although certain differ- 

 ences are perceptible. The distribution of pigment in the skin 

 differs locally. Generally speaking, the trunk is of a deeper 

 colour than the extremities, and, as in the animals, there is a 

 greater accumulation of pigment in the back, especially at the 

 nape of the neck and in the lumbar region than in the chest 

 and abdomen. The part of the body possessing least pigment 

 are the palms of the hands and the soles of the feet, and this is 

 also the case among the coloured races. 



The presence of an accumulation of pigment cells in the 

 corium, giving rise to the Mongolian spots, constitutes no 

 essential point of difference between man and the apes, for 

 they are found in many though not in all apes, but the cells 

 are not confined to the inguinal region. 



The one great distinction of colouring between man and 

 the anthropoids is that of the lips. Among the lower apes the 

 lips are usually brownish black, and even in the gorilla they 

 are of the same dark, blackish colour, with a somewhat polished 

 surface, as the rest of the face. In the chimpanzee the edge of the 

 lower lip is of a dirty flesh-colour, and in the orang a narrow 

 edge of the inner mucous membrane of the mouth is visible. 

 No ape nor any other mammal possesses the red edge of the 

 upper and lower lip which is so eminently characteristic of 

 man. The red colouring of the lips is due to a greater supply 

 of blood in that part and to a certain transparency of the 

 epithelium, this condition being possibly caused by a deposit of 

 eleidin in the epidermis, as in the nails. In the negro the transi- 

 tion zone between the skin and the mucous membrane is much 

 more extensive than in the European and has the same colour- 

 ing as the skin, being very rich in pigment. 1 



Another distinctive human character is the bosom, formed 

 by the development of cushions of fat in the neighbourhood of 

 the mammary glands (see Fig. 56), and the human female alone 

 has a nipple surrounded by an areola. In order to trace the 

 gradual evolution of the mammary glands in the mammals we 

 must go back to the lowest members of the class, namely, the 



1 A.. Oppel, Lehrbuch der vergleich. mikrosk. Anat. d. Wirbeltiere. Jena, 

 G. Fischer, 1900, part 3, p. 52. 



