THE SKIN. 



the corium and the tela subcutanea, which, however, are so blended with each other 

 as to be without sharp demarcation. 



The corium or derma, the more superficial and compact of the connective 

 tissue strata, lies immediately beneath the epidermis from which it is always well 

 defined. With the exception of within a few localities, as over the forehead, external 

 ear and perineal raphe, the outer surface of the corium is not even but beset with 

 elevations, ridges, or papillae, which produce corresponding modelling of the opposed 

 under surface of the overlying epidermis. The pattern resulting from these eleva- 

 tions varies in different regions, being a net-work with elongated meshes over the 

 back and front of the trunk, with more regularly polygonal fields over the extremi- 



FIG. 1147. 



Portion of corium from palmar 

 surface of hand after removal of epi- 

 dermis ; each range includes a double 

 row of papillae, which underlie the 

 superficial cutaneous ridges and en- 

 close openings of sweat glands ; latter 

 appear as dark points along ranges 

 of papillae. X 5. 



Sweat 

 glands 



Small portion of preceding specimen, 

 showing papillae under higher magnifica- 

 tion ; orifices of torn sweat glands are seen 

 between papillae. X 24. 



ties and with small irregular meshes on the face (Blaschko). The best developed 

 papillae are on the flexor surfaces of the hands and feet, where they attain a height 

 of .2 mm. or more and are disposed in the closely set double rows that underlie the 

 cutaneous ridges on the palms and soles above noted. The papillae afford favorable 

 positions for the lodgement of the terminal capillary loops and the special organs of 

 touch and are accordingly grouped as vascular and tactile. 



In recognition of the elevations, which in vertical sections of the skin appear 

 as isolated projections, the corium is subdivided into an outer papillary stratum 

 (corpus papillare), containing the papillae, and a deeper reticular stratum (tunica 

 propria), composed of the closely interlacing bundles of fibrous and elastic tissue 

 that are continued into the more robust and loosely arranged trabeculae of the tela 

 subcutanea. These two strata of the corium, however, are so blended that they 

 pass insensibly and without definite boundary into each other. Although composed 

 of the same histological factors bundles of fibrous tissue, elastic fibres and con- 

 nective tissue cells the disposition of these constituents is much more compact in 

 the dense reticular stratum than in the papillary layer, in which the connective 

 tissue bundles are less closely interwoven. While the general course of the fibrous 

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

 continued upward 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, 



