836 
the posterior margin of the os hyoides even in 
the adult Frog, although they remain for a very 
long while in a cartilaginous condition. The 
two pieces a, a, then speedily become dimi- 
nished in breadth, and the whole shape of the 
os hyoides approximates that of the adult Frog, 
the condition of the pieces marked a, a, forming 
the chief difference between them. This at 
length becomes gradually more slender and 
elongated, assuming at last the shape delineated 
in fig. 26, vol. i. (a), where the permanent and 
complete condition of the os hyoides of this 
Reptile is fully established. 
he different pieces composing the os hyoides 
of a Bird having been already described and 
figured (vide Article Aves, jig. 151), it only 
remains for us in this place to complete our 
review of the hyoid apparatus by examining its 
condition in the Mammiferous races, in which 
it is found gradually to become stripped of 
many parts that before entered so conspicuously 
into the construction of this portion of the 
osseous frame-work of the throat, and assume a 
simplicity of structure that progressively assi- 
milates to the shape it presents in the human 
subject, in which alone indeed the name of 
hyoides is at all applicable. In Man, observes 
Geoffroy, the os hyoides is generally said to 
consist of a body and four symmetric pairs of 
branches or cornua. The anterior cornua (su- 
perior when man stands in the erect posture) 
are reduced to mere rudiments, but in those 
Mammalia that have the head elongated these 
anterior cornua are very largely developed, 
appended from the sides of a special pair of 
bones, the styloids, which, although in mankind 
they are reduced to simple and almost useless 
apophyses, consolidated with the temporal 
bones in the generality of Mammifers, are very 
large and important pieces, so connected with 
the anterior cornua that they are frequently 
regarded as being additional parts of the os 
hyoides. But although in the human body 
these apophyses are comparatively small, and 
are respectively removed, as it were, to their 
proper places, the styloids to the cranial bones, 
and the anterior cornua to the os hyoides, they 
perform the same office of connecting the hyoid 
apparatus to the cranium in Man by the inter- 
position of a cartilage, and in quadrupeds still 
more effectually by an uninterrupted chain of 
bores connected with each other. 
The posterior cornua, each consisting of a 
single piece, resemble each other in office at 
least, in all the Mammalia, forming with the 
body of the os hyoides a horse-shoe figure, to 
which the larynx is appended. The body itself, 
or central portion of the bone, although in the 
human subject only represented by a slight 
tuberosity, will be found in the Rodentia, 
Ruminants, and more especially Solipeds, to 
become very conspicuous, and in the last case 
obviously distinct elements of the skeleton. In 
these Mammalia indeed, the os hyoides is 
found to consist of no fewer than nine pieces, 
without enumerating the styloid bones ; a con- 
dition of complexity almost approaching that 
met with in the Birds and inferior Vertebrata. 
Leaving the consideration of the bones of the 
OSSEOUS SYSTEM. (Comp. Anat.) 
face, and those which enter into the compo- a 
sition of the hyo-branchial apparatus, which 
may be all regarded as forming a succession of 
arches depending from the sides of the cranial 
vertebra, of the transverse processes, of which 
they are indeed regarded by some writers to be 
ee costal prolongations; the anatomist finds 
a more or less extensive series of bones derived 
from the sides of the spinal vertebre, and fre- 
quently arching downwards to enclose and pro- 
tect the viscera either of the thorax or of the 
abdomen, or of both. These lateral appa z 
dages to the spinal column are invariably in 
connection with the transverse processes, of 
which in their simple forms they might seem to — 
be derivations, but when largely developed, as 
for example in the thorax of Mammiferous 
animals, they attain to a prodigious size, form-— 
ing, almost by themselves, the frame-work of 
the thorax, and constituting the paneer agents” 
employed in the performance of the mechanical 
actions connected with the inspiration and ex- 
piration of the air used for the purpose of 
respiration. The pee of the ribs thus 
employed for the formation of a thorax is ex- 
tremely variable in different races. In Man 
and all other Mammalia, in obedience to a law 
at present unexplained, they commence inva- 
riably at the eighth spinal vertebra, counting 
from the skull; but in Birds the whole thorax 
is removed much further backwards in order’ 
allow of the greater elongation of the neck. __ 
Besides the dorsal ribs thus derived from the 
spine, and which exist alone in the human 
subject and in Mammalia generally, anothe; 
series of additional elements is met with in 
Reptiles and in Birds, which must be called 
sternal ribs, and these, conjoined with the la 
enter into the composition of the thoracic cavit 
In Fishes only dorsal ribs are met with, and thes 
are connected bya simple articulating facet to th 
sides of the bodies of the vertebrae placed imme 
diately above the abdominal cavity. Frequenth 
however, the ribs of Fishes have supplements 
bones appended to them, which in the livin 
fish are embedded amongst the lateral musel 
of the body. Sometimes, indeed, these adi 
tional rib-like processes arise immediately fro 
the bodies of the vertebre themselves, giv 
an appearance of complexity to this portion 
the skeleton that is calculated to puzzle | 
young osteologist. In the Cyprinide and 
Herring tribe a small osseous piece is interpo 
between the vertebra and the rib that is 
pended to it; this is obviously a detached t 
verse process. In the Batrachia de 
only are found, and these, even when | 
largely developed, are mere rudiments appen 
to the ends of the transverse processes 0 
vertebree. ) 
In Serpents likewise the enormously 
longed thorax is entirely made up of 
elements, but these, existing as they do a 
along the whole length of the body, and 
moved by an elaborate muscular appat 
perform to a certain extent the office of | 
motive organs, =: 
In the Chelonian and Saurian Reptile 
construction of the thorax becomes much 1 
