GLAXDS OF MUCOUS MEMBEANES 209 



and simple, others larger and compound or cleft into secondary papillse. 

 They serve various purposes ; some of them no doubt minister to the 

 senses of taste and touch, many appear to have chiefly a mechanical 

 office, while others would seem intended to give greater extension to 

 the surface of the corium for the production of a thick coating of 

 epithelium. The villi are most fully developed on the mucous coat of 

 the small intestines. Being set close together like the pile of velvet, 

 they give to the parts of the membrane which they cover the aspect 

 usually denominated " villous." They are in reality little elevations or 

 processes of the superficial part of the corium, covered with epithelium, 

 and containing blood-vessels and lacteals, which are thus favourably 

 disposed for absorbing nutrient matters from the intestine. The more 

 detailed description of the papilljB and villi belongs to the special 

 anatomy of the parts where they occur. 



In some few portions of the mucous membrane the surface is marked 

 with fine ridges which intersect each other in a reticular manner, and 

 thus inclose larger and smaller polygonal pits or recesses. This 

 peculiar character of the surface of the membrane, which has been 

 termed '* alveolar," is seen very distinctly in the gall-bladder, and on a 

 finer scale in the vesiculaa seminales; still more minute alveolar recesses 

 with intervening ridges may be discovered 

 with a lens on the mucous membrane of the 

 stomach (fig. 139). 



Glands of mucous membranes. — Many, 

 indeed most, of the glands of the body pour 

 their secretions into the great passages lined 

 by mucous membranes ; but there are certain 

 small glands which may be said to belong 

 to the membrane itself, inasmuch as they are 

 found in numbers over large tracts of that 

 membrane, and yield mucus, or special secre- F'g- 139.— Portion of Mo- 

 tions known to be derived from particular f^"" .Membrane of the 

 „„ ,• e ,-, 1 r\ -lj:- 11 Stomach, slightly mag- 



portions of the membrane. Omitting local ^,^^^^_ The alveolar pits 

 peculiarities the glands referred to may be and small orifices of the 

 described as of three kinds, viz. : — tubular glands are seen 



1. Tuhiikir glands. — These are minute ^^^*^^' lacker), 

 tubes formed by recesses or inversions of 



the basement membrane, and lined with epithelium. They are usually 

 placed perpendicularly to the surface, and often very close together, 

 and they constitute the chief substance of the mucous membrane 

 in those parts where they abound, its apparent thickness depend- 

 ing on the length of the tubes, which differs considerably in different 

 regions. The tubes open by one end on the surface ; the other end is 

 closed, and is either simple or cleft into two or more branches. The 

 tubular glands are abundant in the stomach, and in the small and 

 large intestines, where they are comparatively short and known as the 

 crypts of Lieberkiihn. They exist also in considerable numbers in the 

 mucous membrane of the uterus. 



2. Small compound glands. — Under this head are here comprehended 

 minute but still true compound glands of the racemose kind, with single 

 branched ducts of various lengths, which open on different parts of the 

 membrane. Numbers of these, yielding a mucous secretion, open into 

 the mouth and windpipe. To the naked eye they have the appearanco 



VOL. II. P 



