384 



HISTOLOGY 



ectoderm 

 epidermis 



SKIN. 



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

 and a mesodermal connective tissue, the corium (Fig. 386). The ecto- 

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

 staining more deeply, and being notably larger than the inner cells. Their 



characteristic dome shape is 

 seen in the figure. The outer 

 layer has been named the 

 epitrichium, since the hairs 

 which grow up through the 

 underlying 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 to the chorionic syncytium. The deeper layer of 

 ectoderm becomes stratified, and gives rise to the hairs, nails, and 



FIG. 386. SKIN FROM THE OCCIPUT OF AN EMBRYO OF Two 



AND ONE-HALF MONTHS. (After Bowen.) 

 The outer layer of dark cells is the epitrichium. 



Duct of a sweat 

 gland. 



Coil of a sweat 

 gland. 



Stratum corneum. 

 Stratum lucidum 



Stratum granulosum. 

 Stratum germinativum 



Stratum 

 papillare. 



Corium. 



Stratum 

 reticulare. J 



Epidermis. 



Stratum subcutaneum. 



FIG. 387. VERTICAL SECTION FROM THE SOLE OF THE FOOT OF AN ADULT. X 25. 



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

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

 These are widely distributed; locally the ectoderm forms the mam- 

 mary glands, ceruminous glands of the ear, ciliary glands of the eyelids, 



