406 



INNERVATION. 



[CHAP. xiv. 



insensibly together, and are not separated from one another by any 

 abrupt limit. Their ultimate texture is indeed essentially the same. 

 Hence the boundary we assign to the skin in this direction is in 

 some measure artificial. Its precise nature will be seen by con- 

 sidering the 



Intimate Structure of the Cutis. The white and yellow fibrous 

 elements of the areolar tissue are both much modified,, to constitute 

 the framework of this layer ; and in different parts of the skin, as 

 may be expected, they exist in different proportions, and in some 

 variety of arrangement. These varieties are not yet made out in 

 all their particulars ; but we believe we may state in general, that, 

 where great extensibility, with elasticity, is required, the elastic 

 element predominates (as in the skin of the axilla) ; and that where, 

 on the contrary, resistance is demanded, the cutis is chiefly com- 

 posed of a dense interweaving of the inelastic white element (as in 

 the sole of the foot). But in all situations the meshes are very 

 close, and the quantity of the mixed fibrous tissues very great, as 

 compared with almost any other part of the body (pp. 77 9). 



The fibres of the yellow element take a generally horizontal course, 

 and lie in multiplied series over one another, branching at very 

 frequent intervals, to join those above, below, and on either side. 

 The resulting meshes are open on all sides, but are most flattened 

 in a direction parallel with the general surface. They are more or 

 less lozenge-shaped, and vary in size not only with the region of 

 the skin in which they are examined, but according to their imme- 

 diate relations with the sudorific ducts, and of other cutaneous ap- 

 pendages which traverse them. This element of the cutis can be 

 easily studied on thin vertical slices, moistened with acetic acid, 

 which acts on other parts, leaving it entire, and, as it were, isolated. 

 (Fig. 77). 



The thick and abundant fibi 

 of the white element twine in great 

 profusion among the interstices 

 just described, but what their pre- 

 cise attachments are it is difficuH 

 to determine. They accompany 

 all the larger vessels and nerves, 

 and invest the several small glands 

 with a loose capsule. 



The gelatine, which may be 

 obtained in considerable quantity 

 from the skin, is derived from 



Yellow fibrous element of the cutis of the 

 axilla. Magnified 320 diameters. this latter part of the CUtis, and 



Fig. 77. 



