Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/16/
8 DIGESTION. 
following pages our main object will be to give 
an account of the function of digestion as it is 
exercised in man and in those animals which 
the most nearly resemble him, referring to 
other animals only so far as it may contribute 
to illustrate or explain the nature of the ope¬ 
ration in the human species. 
In the various divisions of the Mammalia 
the first order of parts may be arranged under 
the five heads of the mouth with its muscular 
appendages, the teeth, the salivary glands, 
the pharynx, and the œsophagus. With the 
exception of the salivary glands, the effect 
of these organs is entirely mechanical ; it con¬ 
sists in the prehension, the mastication, and 
the deglutition of the aliment. The first of 
these organs may be again subdivided into 
three parts, the lips, the cheeks, and the 
tongue ; the lips being more immediately 
adapted for seizing and retaining the food, 
and the others for conveying it, in the first 
instance, to the teeth, for the purpose of mas¬ 
tication, and afterwards to the pharynx, in 
order that it may be swallowed. In this, as 
in every other part of the animal frame, we 
perceive that adaptation of the structure of 
each individual organ to the general habits of 
the animal, which forms a constant subject of 
delight and admiration to the anatomist and 
the physiologist. In animals that feed upon 
succulent and luxuriant herbage the lips are 
capacious, strong, and pendulous, for the pur¬ 
pose of grasping and detaching their food, 
while in those that employ an animal diet, 
where their prey is to be seized and divided 
principally by means of the teeth, the lips are 
thin, membranous, and retractile. Again in 
the muscles that are connected with the cheeks, 
we find the same adaptation, although perhaps 
not in so obvious a degree. We observe that 
animals who receive large quantities of food, 
either in consequence of its being of a less 
nutritive nature, or from any other peculiarity 
in their habits and organization, as well as 
those whose food is of a harder consistence 
and firmer texture, have larger and more 
powerful muscles, both for the purpose of 
moving the jaws with greater force, and for 
acting upon the larger mass of matter which is 
taken into the mouth. 
The principle of adaptation is still more 
remarkable in the teeth. Among the different 
orders which compose the Mammalia, we ob¬ 
serve a general analogy and resemblance be¬ 
tween the teeth, both as to their number, form, 
and relative position, while, at the same time, 
there is so great a diversity in the different 
tribes of animals, that some of the most dis¬ 
tinguished naturalists have regarded these 
organs as the parts the best adapted foi form- 
in°r the basis of their systematic arrangements, 
inasmuch as they afford the most characteristic 
marks of the habits of the animals, and of the 
peculiarities of their other functions. 1 bus, 
by an inspection of the teeth we can at once 
discover whether the individual is intended to 
* Linnaeus, Sys. Nat. t. i. p. 16 et alibi; 
Shaw’s Zool. v. i. Introd. p. vu et ahui. 
employ animal or vegetable food, some of them 
being obviously adapted for seizing and lace¬ 
rating the animals which they acquire in the 
chace or by combat, while the teeth of others 
are obviously formed for the cropping of vege¬ 
tables, and for breaking down and triturating 
the tough and rigid parts of which they prin¬ 
cipally consist. It is with a view to this dou¬ 
ble purpose of prehension and mastication that 
the great division of the teeth into the incisors 
and the molares, the cutting and the grinding 
teeth, depends, the former being of course 
situated in the front of the mouth, the latter 
in the sides of the jaws. The chemical com¬ 
position and mechanical texture of the teeth is 
no less adapted to their office of dividing and 
comminuting the food than their figure and 
position. They are composed of nearly the 
same materials with the bones generally, but 
their texture is considerably more dense and 
compact, while they are covered with an ena¬ 
mel of so peculiarly firm a consistence, as to 
enable them, in many kinds of animals, to 
break down and pulverize even the hardest 
bones of other animals, and to reduce them to 
a state in which they may be swallowed, and 
received by the stomach, in the condition the 
best adapted for being acted upon by the gastric 
juice.* 
At the same time that the alimentary matter 
is subjected to the mechanical action of the 
teeth, it is mixed with the fluids that are dis¬ 
charged from the salivary and mucous glands, 
which are situated in various- parts of the 
mouth. The use of the saliva is to soften the 
food, and thus render it more easily masti¬ 
cated, to facilitate its passage along the pha¬ 
rynx and œsophagus, and perhaps, by a certain 
chemical action, to prepare it for the change 
which it is afterwards to experience, when it is 
received into the stomach.f 
The food, after it has been sufficiently di¬ 
vided by the teeth, and incorporated with the 
saliva, is transmitted, by the act of deglutition, 
into the stomach. There is perhaps no part 
of the system, which exhibits a more perfect 
specimen of animal mechanism than the pro¬ 
cess of deglutition. It consists in the succes¬ 
sive contraction of various muscles, that are 
connected with the contiguous parts, each of 
which contributes to form a series of mecha¬ 
nical actions, which, when connected with 
each other, effect the ultimate object in the 
most complete manner. The muscles of the 
mouth and the tongue first mould the mas¬ 
ticated aliment into the proper form, and trans¬ 
mit it to the pharynx ; this part is, at the same 
time, by the cooperation of other muscles, 
placed in the most suitable position for re¬ 
ceiving the alimentary mass, and transmitting 
it to the œsophagus, while another set of mus- 
* Hatchett, in Phil. Trans, for 1799, p. 328-9 ; 
Berzelius, View of Animal Chemistry, p. 78 ; 
Pepys, in Fox on the Teeth, p. 92 et seq ; Turner’s 
Chemistry, p. 1012. 
t For the opinions that were entertained by the 
older physiologists on this point the reader is re¬ 
ferred to Baglivi, Diss. 2, circa salivam, op. 
p. 412 et seq.; also to llaller, El. Phys. 18. 2. 13.
        

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