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/lit25760/179/
EYE. 
171 
passage of the tendons of the peronæi muscles. 
The apex of the malleolus is directed down¬ 
wards, and is the point of attachment of the 
middle external lateral ligament. 
Structure.—This bone is very light and 
elastic, a property rendered necessary by the 
antagonist muscles which are inserted into its 
opposite surfaces. Its extremities are composed 
of cancellated structure, which extends some 
way to the shaft of the bone. The medullary 
canal, very narrow and irregular, is found only 
in its middle third. 
Developement of the hones of the leg.—The 
tibia begins to ossify somewhat earlier than the 
fibula. Both bones begin to ossify in their 
shafts ; the ossifie point of the shaft of the tibia 
appears about the middle of the second month. 
According to Meckel, in the embryo of ten 
weeks, the fibula is not above half the length of 
the tibia; after the third month the two bones are 
nearly equal. Both bones have an ossifie point 
for each extremity. The superior extremity of 
the tibia begins to ossify towards the termination 
of the first year after birth. The inferior extre¬ 
mity is ossified in the course of the second 
year : the external malleolus is a prolongation 
of the inferior extremity. The union of the 
extremities with the shaft commences by the 
inferior, and is completed from the eighteenth 
to the twenty-fifth year. The ossification of 
the fibula follows nearly the same course, 
excepting that the superior extremity does not 
begin to ossify till the fifth year. 
The tibia constitutes the principal pillar of 
support to the leg. It is placed perpendicu¬ 
larly under the femur, and as the latter bone 
is inclined inwards, it follows that there must 
be an angle formed between these two bones 
at the knee-joint, a very obtuse one, with its 
apex inwards.* It is then by the strength and 
direction of the tibia that the leg firmly sup¬ 
ports the body in the erect attitude ; the fibula 
seems not to contribute at all to the solidity of 
the limb, but is chiefly employed to increase the 
surface of attachment for the muscles of the leg. 
The developement of the tibia and fibula in 
the inferior mammalia is pretty similar to that 
of the radius and ulna. The tibia is always 
fully developed, and, as in man, is the prin¬ 
cipal bone of the leg, its size being pro¬ 
portionate to the weight and strength of the 
animal. Admitting the fibula to be the ana¬ 
logue of the latter bone, we find that, as it 
is rudimentary in the Solipeds and Ruminants, 
so the fibula is in a similar condition in these 
animals. In the former animals this bone is 
applied to the external side of the head of the 
tibia in the form of an elongated stilet, termi¬ 
nating less than half way down in a fine point. 
On the other hand, in Ruminants it is only the 
inferior part of the fibula that is developed ; it 
appears under the form of a small narrow bone, 
extending a very little way upwards, and form¬ 
ing the external malleolus. 
* A preternatural obliquity of the femur causes 
a corresponding divergence of the tibia from the 
perpendicular. When the femur is directed un¬ 
usually inwards, the tibia is directed downwards 
and outwards. 
In Pachydermata the fibula is fully deve¬ 
loped and quite distinct from the tibia, and 
very small in proportion. In Edentata the 
two bones are fully developed, and in the 
Sloths the inferior extremity of the fibula con¬ 
tributes to form the articular surface for the 
astragalus. In Rodentia the two bones are 
united together in the inferior half, as also with 
the Insectivora, particularly in the Mole. In 
many Carnivora these bones are fully developed 
and detached : this is particularly manifest in 
the Phocidæ and the Felidæ. In the Dogs, 
however, the fibula is attached to the posterior 
part of the tibia. 
For the description of the bones composing 
the foot, we refer to the article under that 
head; and for further details on the osseous 
system of the extremities, we refer to the 
articles Osseous System (Comp. Anat.) and 
Skeleton. 
Abnorjnal condition of the bones of the extre¬ 
mities.—A congenital malformation of one or 
more of the extremities is classed by Isidore 
Geoffroy St. Hilaire among what he denomi¬ 
nates “ Monstres Ectromeliens,” of which he 
has three subdivisions : 1st, where the hands 
or feet appear to exist alone, and seem to be 
connected with the trunk without the inter¬ 
vention of all or some of the intermediate 
segments; these he denominates Phocomelesr 
(Çuy.71, Phoca, and p.i\oq, membrum,) from their 
resemblance to the permanent condition of the 
aquatic mammalia : 2d, cases in which there 
are one or more incomplete limbs terminating 
in the form of stumps: to these he gives 
the name Hemimeles: and, lastly, where the 
limb or limbs are wholly absent or scarcely at 
all developed. An interesting case of Phoco- 
melia is recorded by Dumeril ; all the limbs 
were in this condition, owing to the absence 
of the humerus, and forearm bones in the upper 
extremity, and the presence of a very imperfect 
femur, developed only as to the head and tro¬ 
chanters, and a very imperfect tibia in the lower 
extremity. The clavicle and scapula were pre¬ 
sent, but presented some irregularities of form.* 
The congenital absence of these last bones is 
rare excepting where the other bones of the 
limb are also absent. 
It would be inconsistent with the objects of 
this article to prosecute this subject further ; we 
therefore refer for further details to the article 
Monstrosity. 
For Bibliography, see that of Anatomy 
(Introduction). 
(R. B. Todd.) 
EYE, (in human anatomy), opôaTytoç, orga¬ 
non visus ; oculus. Fr. Œil; Germ, das Auge ; 
Ital.OccAio.—The human eye is a hollow sphere, 
about one inch in diameter, with a circular 
aperture in the anterior part about one-fifth of 
this sphere in breadth, filled by a transparent 
convex portion called the cornea, through which 
the light is transmitted. Within this hollow 
* Bull, de la Soc. Philomath, t. iii., quoted iu 
Geoff. St. Hilaire’s A nom. de l’Organization, t. ii. 
p. 211.
        

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