268 



Elementary Biology. 



FIG. 129. VERTICAL SECTION SKIN OF 

 RAN A. (Owen ) 



swallowing. The microscopic structure of skin proper and 

 mucous membrane may be best considered together. The 

 skin consists of a series of layers of cells, the superficial 

 layers being composed of flat plates or squames and the 

 deeper layers of more rounded or polygonal cells. To 

 this portion of the skin is given the name of epidermis. 



The epidermis rests on, 

 and is organically con- 

 nected with the dermis, 

 which is composed chiefly 

 of fibrous tissue, blood- 

 vessels, and nerves, 

 amongst which are im- 

 bedded, especially next the 

 epidermis, a large number 

 of irregular pigment cells. 

 The dermis is elevated 

 into a series of vascular 

 papillae which project into 

 the epidermis. In the 

 dermis, and with their 

 ducts piercing and opening 

 on the surface of the epi- 

 dermis, are many subcu- 

 taneous or mucous glands, 

 already referred to. The 

 subcutaneous tissue is 

 separated from the under- 

 f . , . lying muscles of the bodv- 



A, vertical section; e, superficial layer of i O 



epidermis; b, deep layers of epidermis ; \yall by a larSje lymph 



a, layer of pigment cells : c, dermis d, 



mucus gland ; g, connective tissue ; f, SpaCC. 



The mucous membrane 



of the buccal cavity does not differ essentially from the 

 skin in structure ; the layers of cells are, however, fewer in 

 number, the pigment cells are absent, and the vascular 

 supply is more abundant. We shall find, later on, that the 



