342 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



vascular and nerve papillae that fit into depressions 

 on the lower surface of the epidermis. The two 

 layers of the dermis pass into each other without any 

 sharp line of demarcation. In both layers there is 

 an abundance of connective-tissue fibers, both elastic 

 and non-elastic, forming what has been termed areo- 

 lar tissue. These fibers form bundles that interlace 

 to produce a network, particularly in the reticular 

 or deep portions. In the meshes of this reticulum 

 are to be found the bodies of the sweat glands, and a 

 variable amount of adipose tissue, while hair follicles 

 with their sebaceous glands find lodgment in the 

 dermis with greater regularity. It is the dermis , 

 and particularly the areolar tissue, that gives elas- 

 ticity and mobility to the skin. The epidermis is 

 not very elastic, consequently wrinkles of the epi- 

 dermis are formed when the fat is absorbed, and 

 also in old age, by shrinkage of the areolar tissue. 



A variable amount of muscle is everywhere present 

 in the dermis. Smooth muscle is associated with 

 the hair follicles, forming the arrector pili muscle. 

 In the face and neck voluntary muscle fibers may be 

 traced into the papillary layer, while a third set of 

 muscle elements is associated with the sweat glands. 

 The latter is of the smooth variety and will be de- 

 scribed along with the sweat glands. 



The dermis everywhere is very vascular. Blood- 

 and lymph- vessels ramify freely through it, but in 

 no case do they enter the epidermis. Nerve fibers, 

 on the other hand, enter the Malpighian layer of the 

 epidermis and arborize around and between the 

 epithelial cells. In the dermis these fibers form an 



