380 



THE SKIN AND ITS APPENDAGES. 



All these cell layers consist of prickle cells, and for this reason the 

 stratum Malpighii is sometimes known as the stratum spinosum. 

 When these cells are isolated by certain methods, their surfaces are 

 seen to be provided with short, thread-like processes. In section 

 the cells appear to be joined together by their processes. Since it 

 has been proved that the processes of adjacent cells do not lie side 

 by side, but meet and fuse, they must be regarded as belonging alike 

 to both cells. Between the fused processes, which are known as 

 intercellular bridges, there exists a system of channels which is in 

 communication with the lymphatic system of the corium. The 

 prickles just mentioned are variously regarded by different investi- 

 gators ; some considering them to be exclusively protoplasmic 



Fig. 303. Under surface of the epidermis, separated from the cutis by boiling. The 

 sweat-glands may be traced for a considerable part of their length ; X 4 : a > Sweat- 

 gland ; b, longitudinal ridge ; c, depression ; d, cross-ridge. 



processes of the cells, others regarding them as derived from the 

 membranes of the cells composing the stratum Malpighii. Ranvier 

 and others ascribe a fibrillar structure to the peripheral portion of 

 the cellular protoplasm, and, according to them, these fibrillae, 

 surrounded by a small quantity of indifferent protoplasm, form 

 the processes. Ranvier has also shown that such fibrillae may 

 extend from one cell around several others before reaching their 

 ultimate destination in other cells at some distance. (Fig. 305.) The 

 cells of the stratum granulosum contain peculiar deposits of a sub- 

 stance to which Waldeyer has given the name of keratohyalin. 

 This substance occurs in the form of irregular bodies varying in size 

 and imbedded in the protoplasm. The nuclei of such cells always 



