THE SKIN. 555 



the papillary layer they disappear altogether. The bundles of 

 the derma have a certain regularity of arrangement, as is demon- 

 strated by the researches of C. Langer. This investigator 

 punctured the skin with a shoe-maker's awl, and after the with- 

 drawal of the instrument observed, in every instance, instead of 

 round holes, longitudinal clefts, regularly distributed over the 

 entire surface of the body. There are a few places where the 

 awl produces irregular jagged openings in the tissue of the 

 derma ; these are most marked in localities where the derma is 

 closely attached to the subjacent tissues. The same investigator 

 found that the striae of the skin of the abdomen and upper part 

 of the thighs, produced by over-extension, usually in pregnancy, 

 are caused by stretching in a horizontal direction of the bundles 

 of the connective tissue of the derma. The blood-vessels also 

 assume a horizontal course, following the stretched bundles. The 

 epithelial cover remains unchanged. 



In the derma, the connective tissue is mixed with a varying 

 amount of muscles. The striped variety is seen in the skin of 

 the face and the lateral aspect of the neck, where the lowest 

 bundles connect with striped muscle-fibers, often in a reticular 

 arrangement. In many animals the derma has an almost con- 

 tinuous layer of striped muscles, the so-called panniculus carnosus, 

 which enables these animals to produce voluntary movements 

 of the skin. Bundles of smooth muscle-fibers are scattered 

 throughout the derma, either in a reticular or fan-like arrange- 

 ment, or in the shape of single oblique bundles. The reticular 

 arrangement of smooth muscle-bundles presents itself in the 

 skin covering the nipple and its areole, the penis and the 

 scrotum. In the skin of the penis the direction of the muscle- 

 bundles is mostly circular, in the scrotum antero-posterior. The 

 fan-like arrangement, and that in single bundles, occurs all over 

 the skin, the muscles, so-called arrectores pilorum, being every- 

 where in close relation to the hair-follicles. According to W. 

 Tomsa the connection between the smooth muscle-fibers and the 

 tissue of the derma is established by elastic fibers, which are 

 twined around the muscle-bundles. This relation is specially 

 marked in the arrectores pilorum. The connective tissue en- 

 sheathing the larger coils of sweat-glands exhibits smooth 

 muscle-fibers, which produce an almost continous layer around 

 the sweat-glands of the axillae. 



The papillary layer i. e., the outermost portion of the derma 

 is composed of delicate fibers of connective tissue, not distinctly 



