312 



HISTOLOGY. 



SKIN. 



The skin (cutis] consists of an ectodermal epithelium, the epidermis, 

 and a mesodermal connective tissue, the corium (Fig. 358). The ecto- 

 derm is at first a single layer but soon it becomes double, the outer cells 



staining more deeply, and 



fpidennis 



being notably larger than 

 the inner cells. Their char- 

 acteristic dome shape is 

 seen in the figure. The 

 outer layer has been named 

 the epitrichium since the hairs which grow up through the under- 

 lying epithelium do not penetrate it, but cause it to be cast off. The 

 epitrichium has been found on the umbilical cord and in places on the 

 amnion. It may possibly be related with the chorionic syncytium. The 



" | mesodern 



' corium 



FIG. 358. SKIN FROM THE OCCIPUT OP AN EMBRYO 



OF 2^ MONTHS. (After Bowen.) 

 The outer layer of dark cells is the epitrichium. 



Stratum corneum 

 Stratum lucidum 



Stratum granulosum 

 Stratum germinativum 



Epi- 

 dermis. 



Duct of a sweat 

 gland. 



Coil of a sweat 

 gland. 



Stratum 

 papillare 



Corium. 



Stratum 

 reticulare J 



Artery. 

 Fat tissue. 



Stratum subcutaneum. 



FIG. 359. VERTICAL SECTIOX FROM THE SOLE OF THE FOOT OP AN ADULT. X 25. 



deeper layer of ectoderm becomes stratified, and it gives rise to the hairs, 

 nails, and enamel organs. It also produces two types of glands, the 

 sebaceous glands which are usually connected with hairs, and the sweat 



