cc MUCOUS MEMBRANES. 



inclose larger and smaller polygonal pits or recesses. This peculiar cha- 

 racter of the surface of the membrane, which might be called " alveolar," 

 is seen very distinctly in the gall-bladder, and on a finer scale in the vesi- 

 culse seminales ; still more minute alveolar recesses with intervening ridges 

 may be discovered with a lens on the mucous membrane of the stomach 

 (fig. evil.). 



Glands of mucous membranes. Many, indeed 



Fig. CVII. 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 mem- 

 brane, and yield mucus, or special secretions 

 known to be derived from particular portions of 

 the membrane. Omitting local peculiarities the 

 Fig. CYir. PORTION OP Mu- glands referred to may be described as of three 

 cous MEMBRANE OF THE w d j 



STOMACH, SLIGHTLY MAG- ' 7 , . 7 m . . . . 



NIFIED. The alveolar pits * Tubular glands. These are minute tubes 



and small orifices of the formed by recesses or inversions of the base- 

 tubular glands are seen ment 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 depending 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 loculated, or even 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 Lieber- 

 kiihn. 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. They have the appearance of small solid bodies, 

 often of a flattened lenticular form, but varying much both in shape and 

 size, and placed at different depths below the mucous membrane on which 

 their ducts open. The glands of Brunner, which form a dense layer in the 

 commencing part of the duodenum, are of this kind. 



3. Solitary and agminated glands, conglobate glands (Henle), follicular 

 glands (Kolliker). Found in various parts of the alimentary mucous mem- 

 brane, also in the palpebral conjunctiva. They may be single (solitary 

 glands), or in patches (agminated glands). Their structure is well known, 

 but, although they are called glands, their function is still enigmatical. 

 They are small sacs reaching down into the submucous tissue, closed and 

 covered above by the mucous membrane. Within is fine retiform tissue, 

 supporting radiating blood-capillaries, with bodies like lymph-cor- 

 puscles in the meshes, and communicating with a similar tissue (lymphoid 

 tissue) diffused in the adjacent part of the membrane ; for, although they 

 do not open on the surface, their reticular capsule rarely forms a perfect 

 inclosure. Several of these saccules are sometimes placed round a recess of 



