THE MEMBRANES. 475 



seat of the sexual impulse; but this function cannot yet be regarded 

 as established. 



Pathological States of the Nervous Centres. 



Certain pathological conditions of the nerve-fibres and the nerve- 

 cells have already been specified (pp. 433 and 437). The encephalon 

 and cord are also affected by softening and various other abnormal 

 states as from the development of tumors, &c. But the consequent 

 lesions of motion, sensation, and the intellectual faculties, are too 

 numerous and complicated to be described here. 



CHAPTER XI. 



THE MEMBRANES.' 



r 



THE synovial membranes (p. 344), the vaginal sheaths, and the 

 bursae mucosse (p. 418, 3), have already been described. Those to 

 be described in this chapter are: 



1. The cutaneous membrane, or skin. 



2. The mucous membranes. 



3. The serous membranes. 



Each of these consists of the same histological elements from 

 within outwards; viz., 1, the corium; 2, the basement-membrane; 

 and 3, the epithelium. Thus no tissues, not already described, 

 occur in them. 



Both the skin and the mucous membranes present elevations and 



Fig. 315. 



Typical forms of papillae of the skin and mucous membrane, and intestinal villi. a. Basement- 

 membrane. 6. Epithelial layer of secreting cells, mostly detached, c. Layer of capillary vessels in 

 the corium of the skin or mucous membrane, d. Simple papilla or villus. e, f. Compound (branched) 

 papillae. 



depressions on their surface; the former being termed papillas and 

 villi, and the latter, glands. Fig. 315 represents the forms of the 

 papilla, and Fig. 316 of the glands. 





