THE SKIN. 317 



lacing bundles of fibrous and elastic tissue that are continued into the more 

 robust and loosely arranged trabeculae of the tela subcutanea. The strata of 

 the corium, however, are so blended that they pass insensibly and without 

 definite boundary into each other. Although composed of the same histo- 

 logical factors bundles of fibrous tissue, elastic fibres and connective tissue 

 cells their disposition is much more compact in the dense reticular stratum 

 than in the papillary layer. While the general course of the fibrous bundles 

 within the corium is parallel or oblique to the surface, some strands, contin- 

 ued upwards from the underlying subcutaneous sheet, are vertical and traverse 

 the stratum reticulare either to bend over and join the horizontal bundles, or 

 to break up and disappear within the papillary stratum. The elastic tissue, 

 which constitutes a considerable part of the corium, occurs as fibres and net- 

 works. Within the reticular stratum these form robust tracts corresponding 

 with the general arrangement of the fibrous bundles. Towards the surface 

 of the corium, the elastic fibres become finer and more branched and beneath 

 the epidermis anastomose to form the delicate but close subepithelial elastic 

 network. 



The tela subcutanea, the deeper layer of the connective tissue por- 

 tion of the skin, varies in its thickness and in the density and arrangement 

 of its component bundles of fibre-elastic tissue, with the amount of fat and 

 the number of hair-follicles and glands lodged within its meshes. The latter 

 are irregularly round and enclosed by tracts of fibrous tissue, some of which, 

 known as the retinacula cutis, are prolonged from the corium to the deepest 

 parts of the subcutaneous stratum. Here they often blend into a thin but 

 definite sheet, the fascia subcutanea, which forms the innermost boundary 

 of the skin and is connected with the subjacent structures by strands of 

 areolar tissue. Where such loose connection is wanting, as on the scalp, 

 face, palms and soles, the skin is intimately bound to the underlying mus- 

 cles or fasciae and lacks the independent mobility that it elsewhere enjoys. 

 The integument covering the eyelids and penis is peculiar in retaining to 

 a conspicuous degree its mobility although devoid of fat. Where the latter 

 is present in large quantity, the term panniculus adiposus is often applied to 

 the tela subcutanea. 



In places in which the skin glides over unyielding structures, the inter- 

 fascicular lymph-spaces of the tela subcutanea may undergo enlargement 

 and fusion, resulting in the production of the subcutaneous mucous bursa. 



In addition to the strands of involuntary muscle associated with the hairs 

 as the arrectores pilorum, unstriped muscular tissue is incorporated with the 

 skin in the mammary areolae and over the scrotum and penis (tunica dartos). 

 The facial muscles having largely cutaneous insertions, the skin covering the 

 face is invaded by tracts of striated muscular tissue that penetrate as far as 

 the corium. 



The Epidermis. The epidermis or cuticle, the outer portion of the 

 skin, consists entirely of epithelium and, being partly horny, affords protec- 

 tion to the underlying corium with its vessels and nerves. The thickness of 

 this layer varies in different parts of the body. Commonly from .08 

 . 10 mm., it is greatest on the flexor surfaces of the hands and feet, where it 

 reaches from .5-. 9 mm. and from i. 1-1.3 mm - respectively. Where exposed 

 to unusual pressure, as on the palms of laborers or on habitually unshod 

 soles, the epidermis may attain a thickness of 4 mm. 



The cuticle consists of two chief layers, the deeper stratum germina- 

 tivum, containing the more active elements, and the stratum comeum, the 

 cells of which undergo cornification. Between these layers lies a third, the 



