STRUCTURE OF THE MUCOUS MEMBRANE. 287 
villous (fig. 3) ; the former being found in the stomach and 
large intestine, the latter in the small intestine. 
The alveolar mucous membrane is so named from present- 
ing a surface made up of minute depressions in the form of 
pens or cells, separated by septa: these depressions being 
the alveoli. The villous mucous membrane, on the other 
hand, is characterised by projections of its surface, the pro- 
jections being termed villi. 
These terms are simply expressions for the idea which is 
given by a coarse observation of the surface, and have little 
reference to the structure which gives rise to such appear- 
ances; for if we adopt the idea of distinguishing the mucous 
membrane by the projections developed on its surface, as in 
the case of the villi, we ought, correctly, to term the alveolar 
membrane reticulated, distinguishing the prominences on its 
surface and not its depressions ; for the prominences or 
septa are elevations of the membrane analogous to the villi, 
the alveoli being merely the spaces between the septa and the 
floor of the alveoli, the ground surface of the membrane. 
The term “ reticular,” therefore, seems to me preferable to 
“ alveolar,” for several reasons, namely, in the first place, as 
conveying the idea of prominence or development from the 
surface, and therefore corresponding with the term “ villous,” 
applied to another part of the same membrane ; secondly, as 
truly representing the structure, for the septa do, in reality, 
form one continuous network over the whole surface, the 
areolae of this network being the alveoli ; thirdly, as sup- 
porting the analogy between the alimentary and other 
mucous membranes ordinarily described as “reticulated,” for 
example, that of the gall-bladder and vesiculae seminales; 
and, lastly, as extending the analogy of structure to inferior 
animals, as the ruminant, wherein one division of the stomach 
is termed, from the presence of a magnified representation of 
the same structure, “ reticulum;” and to the camel, where the 
deep spaces or alveoli between the septa are so remarkable, 
and perform so important an office in relation to the habits of 
the animal. 
RETICULAR MUCOUS MEMBRANE. 
Stomach . — In the stomach, as already said, the mucous 
membrane is reticular ; the raised portion of the membrane 
forming a fine net work (reticulum) over its whole surface, 
and constituting the septa, the areolae of the net-work being 
the alveoli. The amount of projection of the reticular frame, 
