CUTANEOUS APPENDAGES 271 



The periderm forms a layer of peculiar dome-shaped cells with flat- 

 tened margins and a vesicular center. It continues to form the super- 

 ficial layer of the epidermis until about the sixth month, when it is 

 lost by desquamation. The germinal layer consists of a deep stratum of 

 cylindrical cells and one or two superficial strata of spheroidal vesicular 

 cells. The latter are known as the stratum intermedium. By the fifth 

 or sixth month cell differentiation has advanced in the intermediate 

 portion until cornification can he distinguished in its superficial cells. 



Further development is analogous to the growth of the mature epi- 

 dermis; new cells are rapidly formed in the deeper portion, stratum 

 germinativum, and are steadily pushed toward the surface, their migra- 

 tion being either accompanied by slight, or later by more pronounced 

 cornification, which in the latter case gives rise to the stratum granulo- 

 sum, stratum lucidum, and horny layer, but in the former produces 

 only relatively slight flattening of the superficial cells without the ap- 

 pearance of keratin or the disappearance of the nucleus. 



The derma arises from the superficial layers of the mesoblast as 

 ordinary connective tissue, in which the appendages of the skin make 

 their appearance as ingrowths from the epidermis. Certain mesenchymal 

 cells form the smooth muscle fibers of the arrectores pilorum muscles 

 and of the derma of those locations where muscle is present in the mature 

 skin. Other mesenchymal cells produce the fat lobules of the subcu- 

 taneous tissue. Papilke appear during the fourth or fifth month but 

 do not attain their completed development until much later. 



CUTANEOUS APPENDAGES 



The cutaneous appendages include the sudoriparous glands, the nails, 

 the hairs, and the sebaceous glands. 



SUDORIPAROUS GLANDS 

 (Glandules Sudori/ninr, ^irr/it (Hands) 



The sudoriparous glands occur in all portions of the skin, but more 

 abundantly in certain locations, e.g., palms of the hands and soles of 

 the feet, where their number has been estimated at between two and 

 three thousand to the square inch axilla?, groin, and circumanal re- 

 gion. Over the back, where they are least numerous, their number is 

 said to be less than five hundred to the square inch. They are long, 

 coiled or convoluted, tubular glands whose secreting portions lie in the 



