290 THE SKIN 



Sebaceous glands of the scalp may become cystic through occlusion of 

 the duct and form wens. 



Development. The sebaceous glands are developed as minute epithe- 

 lial buds from the sides of the hair columns or from the deeper surface 

 of the epidermis. These buds soon assume the characteristic flask shape 

 and later become hollowed out by fatty metamorphosis of their central 

 cells. By this process also their lumen is eventually made continuous 

 with that of the follicle. Secondary saccules of the sebaceous glands are 

 developed in a similar manner by outgrowing germs which appear near 

 the constricted neck portion of the primary saccule. 



BLOOD SUPPLY OF THE SKIN 



The larger arteries supplying the skin lie in the subcutaneous tissue. 

 From these vessels branches pass toward the surface, giving off lateral 

 twigs to the rich capillary plexuses in the subcutaneous connective and 



FIG. 279. RECONSTRUCTION OF THE CUTANEOUS BLOOD-VESSELS. 



a, epidermis; 6, derma; c, subcutaneous tissue; d, deep, and e, superficial arterial 

 plexus; f-i, successive venous plexuses. X 9}^. (After Spalteholz.) 



adipose tissues and about the sweat glands, hair follicles, and sebaceous 

 glands. These arteries continue their course to the deeper part of the 

 corium, where they form an anastomosing cutaneous plexus of small 



