Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/81/
AG K. 
69 
that of inferior animals. The urine is retained 
a shorter time in the bladder ; it is more aqueous 
and less impregnated with saline and animal 
ingredients than in after life ; there is also a 
particular deficiency of urea. Of the intes¬ 
tines we have already spoken ; their contents 
are copious but less feculent than they after¬ 
wards become. The perspiration affords a si¬ 
milar character to that of the other excrementi- 
tious secretions, being more aqueous, less sa¬ 
line, and less odorous. On the whole it may 
be said that less activity is indicated in the 
egestive than in the ingestive system. 
Of the defensive organs, or those which 
are exposed to surrounding agents, we may 
remark, in general terms, that although fully 
adequate to the demands of the infant under 
the circumstances of his existence, they acquire 
a development proportionate to his growing in¬ 
dependence of the care of others. The skin 
increases in firmness, and the epidermis in thick¬ 
ness ; the sebaceous follicles become larger and 
more numerous, and the hair is more abundant. 
There is a portion of the nervous system 
which we have every reason to consider more 
related with the functions which have been just 
reviewed, than with those of the animal life, and 
which might à priori be expected to bear 
a corresponding ratio of developement. We 
allude to the ganglions; they appear to be 
fully formed at birth, but what changes they 
undergo between that period and maturity we 
do not profess to know. In old age their 
tissue is found hardened, shrunken, and of a 
greyish colour. (Bichat.) 
The changes that we have next to take 
notice of are of a totally different character 
from the foregoing. They consist not merely 
in augmentations of size, correspondently with 
the general increment of the body, or in modi¬ 
fications of organs according to the altered 
circumstances under which they have to act, 
but in processes essential to the completeness 
of certain organs. These are the parts em¬ 
ployed in locomotion, voice, sensation, and 
thought. We shall begin with the osseous 
system. 
Bones are not subservient to locomotion 
only ; they have, in some parts of the body, 
the important office of enclosing and defending 
from external injury the more delicate organs of 
the system. We shall find, therefore, that in 
the young animal, according as they fulfil the 
one office or the other, their development will 
differ. But whatever be the functions of the 
bones, they require, for the perfection of that 
function, three mechanical properties,—firm¬ 
ness, lightness, and tenacity. They must not 
admit of flexion, and, at the same time, the 
density of their substance must not render 
them cumbrous by weight, or brittle in texture. 
To present these three conditions, the organs in 
question consist of two principal ingredients, 
an animal matter and an earthy matter, most 
intimately interwoven ; the one preventing such 
vibrations as would occasion risks of fracture, 
the other affording the necessary strength in 
supporting weights, and in resisting the divellent 
tendencies of antagonist muscles. The pro¬ 
portion which these parts bear to each other 
varies with the ages of the human subject. 
Viewed as a part of the system devoted to the 
life of relations, bones are used as pillars of 
support, as levers in various attitudes and mo¬ 
tions, and as points d'appui to the muscles and 
tendons. On examining the constitution of 
these portions of the osseous system in the 
new-born infant, we find the quantity of cal¬ 
careous salts comparatively small, and even 
the animal substance softer than in later pe¬ 
riods, in consequence of the greater ratio of 
gelatine. In growth these proportions undergo 
a gradual alteration ; the gelatine is diminished, 
the cartilage becomes firmer, and both give 
way to the deposition of earthy particles : in 
the increase of density produced by this de¬ 
position consists the process of ossification. 
To particularize the incompleteness of the 
osseous system would require us to enter upon 
the anatomy of almost every bone in the body, 
an investigation incompatible with the limits of 
this article. Some idea of it may be obtained 
from the fact that all the epiphyses of the long 
bones, and the greater number of the apophyses 
are as yet but cartilaginous ; they derive their 
ossification, not from an extension of the pro¬ 
cess in the bones to which they are attached, 
but from ossifie centres within their own 
spheres. In the tarsus the only bones in 
which ossification has commenced are the as¬ 
tragalus and os calcis. The carpus is entirely 
cartilaginous. The os innominatum of the pel¬ 
vis consists of three separate bones ; ossifica¬ 
tion has but just commenced in the descending 
ramus of the pubis, and the ascending part of 
the ischium ; and the consolidation of the pel¬ 
vis is not complete till after the thirteenth year. 
The long bones have no central medullary 
cavity in the early periods of intra-uterine life ; 
but in the foetus at its full term, the animal 
matter which occupied that space has begun to 
be absorbed, and the deposition of osseous 
matter takes place in the form of a cylindrical 
sheath, so that the canal exists at this period, 
though in an incomplete state. The medullary 
canal is analogous to the cells of the short and 
flat bones, and of the extremities of the long 
bones, which are also incomplete in infancy. 
The shape of the cylindrical bones is mani¬ 
festly different from that which they afterwards 
assume ; thus there is a much smaller dispro¬ 
portion between the diameters of the extremi¬ 
ties and that of the shaft ; the surface is less 
furrowed by sinuses or roughened by ridges; 
differences exactly corresponding to the imper¬ 
fect development of the muscles, which, when 
more bulky in their middle portions, require a 
larger space for their accommodation about 
the body of the bone, and when stronger in 
contraction, require attachments that will match 
them in firmness. The osseous system is not 
complete till after the age of twenty. 
There is no part of the skeleton in which we 
have a more striking illustration of its gradual 
development than in the bones of the face and in 
the cranium. It is not till the seventh year that 
a separation begins to take place between the 
tables of the skull, that the frontal sinus begins