THE SKIN. 



131 



r hich 



From these the lymph is carried away by still larger vessels, 

 course in the subcutaneous tissue. 



The appendages of the skin are the nails, the hairs, with their 

 sebaceous glands and the sweat-glands. They are all developed as 

 thickenings and downgrowths of the Malpighian layer of the epidermis. 



FIG. 154. --SECTION ACROSS THE NAIL AND NAIL-BED. (100 diameters. ) (Heitzmann.) 

 P. ridges with blood-vessels ; , rete mucosum ; N, nail. 



The nails are thickenings of the stratum lucidum of the epidermis, 

 which are developed over a specially modified portion of the corium, 



(which is known as the bed or matrix of the nail, the depression at the 

 posterior part of the nail-bed from which the root of the nail grows 

 being known as the nail-groove. The distal part of the nail forms the 

 free border, and is the thickest part of the body of the nail. The horny 

 substance of the nail (fig. 154, N) is composed of clear horny cells, 

 each containing the remains of a nucleus ; it rests immediately upon 

 a Malpighian layer (B) similar to that which is found in the epidermis 

 generally. The corium of the nail-bed is beset with longitudinal 

 ridges instead of the papillae which are present over the rest of the 

 skin; these, like the rest of the superficial part of the corium, are 

 extremely vascular. The nails are developed in the fo3tus at about 

 the third month, the groove being formed at this time in the corium, 

 and the nail-rudiment appearing in it as a thickening of the stratum 

 lucidum, which lies over the bed. It becomes free in the sixth month, 



