840 
ployed in constructing the shoulder-joint, but 
is by no means constantly present. In Fishes its 
existence as a distinct bone is not recognisable ; 
but in all the Reptilia it constitutes a highly 
pe eo piece of the skeleton. 
n Birds the clavicles, in consequence of the 
elasticity and strength indispensable in the 
composition of the bony framework of the 
shoulder in animals constructed for flight, pre- 
senta very peculiar arrangement, being generally 
solidly anchylosed to each other in the mesial 
line, where they meet, forming a single bone, 
to which the name of furculum is generally 
given. In Birds, however, that are not organized 
for flight, such as the Ostrich, this peculiarity 
is dispensed with, and two distinct clavicles 
are found articulated with the sternum, as in 
the generality of Vertebrata. 
In the Mammalia again the clavicles are 
much reduced in importance and frequently are 
entirely wanting, as in all the pachydermatous 
races. It is only when extensive movements 
are required in the anterior limbs, either for the 
ocr of flight, climbing, digging, or pre- 
ension, that clavicles are interposed between 
the shoulder of a quadruped and the anterior 
portion of the sternum, so as to form a kind of 
pivot on which the whole shoulder moves, and 
in the human subject the freedom of motion 
obtained for the arms and hands by this arrange- 
ment contrasts strongly with the fixed condition 
of the shoulder, both of Birds and Reptiles. 
The coracoid bone, forming the third element 
employed in constructing the shoulder-joint of 
Vertebrate animals, is only fully developed in 
the Reptilia and in Birds. In Fishes it is but 
doubtfully represented by two beny pieces 
already referred to; but in all the Batrachian 
and Saurian Reptiles it constitutes the strongest 
support of the shoulder, abutting on the sternum 
on the one hand, and on the other firmly con- 
nected with the shoulder-joint. In the Chelo- 
nian Reptiles, too, the coracoids are very large, 
and remarkable on account of the extraordinary 
inversion of the skeleton of these animals, the 
scapulz being here actually placed inside the 
thorax within the ribs, and fixed by ligaments 
to the sides of the bodies of the vertebre ; 
while the coracoid bones, equally placed within 
the thoracic box, are similarly circumstanced as 
regards the p/lastron or enlarged sternum that 
covers them inferiorly. 
In Birds the coracoid bones are of peculiar 
strength and solidity, serving as buttresses to 
support the shoulder against the vigorous trac- 
tion of the enormous pectoral muscles. It 
stretches trom the anterior margin of the 
sternum, with which it is firmly articulated, to 
the junction of the scapula and clavicle, where 
it assists in forming the glenoid cavity. 
Throughout all the Mammalia, with the 
exception of the Monotremata, the coracoid 
bones are wanting or only represented by a 
small apophysis, consolidated with the neck of 
the scapula, as is the case in the human skeleton, 
to which the term coracoid process has been 
generally applied. 
The humerus, the first bone of the anterior 
extremity, is invariably a single bone interposed 
OSSEOUS SYSTEM. (Come. Anat.) 
between the glenoid cavity and the forearm. It 
is invariably present throughout all the Reptilia, 
excepting of course the apodal Ophidian races, 
and is at once recognisable by the anatomist. 
In Birds, likewise, the humerus offers nothing 
remarkable except the mechanical arrangement 
of its articular extremities. a 
Neither in the Mammalia is there any aberra- — 
tion from the common type of structure, the © 
only variations being in the length, form, or 
proportions of this piece of the skeleton, adapt- 
ing it to the necessities of the different races of 
Mammifera. 
The forearm, or second division of the upp 
extremity, is normally made up of two bon 
called respectively the udna and the radi 
These are incomparably most complete in t 
human subject, where their admirable conn 
tions with the humerus, with each other, 
with the hand, are amongst the most strikin 
instances of perfect mechanism met with in tht 
animal creation. ; 
In Fishes and in the Batrachian F 
they are most imperfectly develo nc 
invariably anchylosed together. In the Ch 
nian and Saurian Reptiles they become ¢ 
distinct from each other, but the movements 
pronation and supination are extremely limi 
The ulna of Birds 1s the principal bone of 
forearm, while the radius is a 
co? distinguishable by the relations it b 
to the other parts of the wing ; here likewise, 
consequence of the uses of the anterior extt 
mity as instruments of flight, these bones ¢ 
almost immoveably fixed in a state of pronati 
In the unguiculate Quadrupeds general 
the ulna and radius are separate bones, 1 
a few exceptions, such as the iropte 
where one bone only constitutes the fe 
but amongst the Ungulata they are frec 
more or less consolidated and fused toge 
towards their distal extremities, as, for exam 
in the Ruminants and in the Solidungula, 
The carpus, forming the third division of 
upper extremity, generally consists of sever 
short and thick bones firmly bound toget 
ligaments, but allowing of sufficient motion 
tween each other to afford a slightly mow 
basis to support the parts composing the 
either to prevent concussion in walking 
permit increased mobility to the fingers. 
most completely developed, as they are 
in the human subject, they are eight in nu 
to which names indicative of their 
been applied, such as scaphoides, unas 
Jorme, pisiforme, trapezium, trape: 
num, and unciforme ; but these names ¢ 
be supposed to be applicable to the carpal 
of other Vertebrata, in which they pres 
many varieties both in their shape and’ 
as frequently to be quite unrecogn 
analogues of each other, their nt 
varying most considerably, either on 
of the coalescence of elements origina 
tinct, or from their total suppression. 
The bones of the carpus in Fishes are 
rally represented by four or five small 
interposed between the bones of the fo 
and the pectoral fin. With these bom 
