OSSEOUS SYSTEM. (Comp. Anat.) 
attached to the extremity of 
the upper portion of one of 
the three last branchial 
arches. 
Condition of theos hyoides 
én Reptiles.—The condition 
of the os hyoides ina per- 
fect Reptile is very simple 
when compared with that 
of the Fish, or even, as is 
most strikingly apparent in 
the Raa bs ails, 
with that which it exhibits 
previous to the accomplish- 
ment of the metamorphosis 
which changes the mode of 
respiration from that ofa fish 
into that of the Frog. In the 
adult Reptile, indeed, the 
_ composition of this bone 
gives no indication of its pre- 
vious complexity of struc- 
ture, consisting only of the 
remains of the anterior cor- 
nua (26, a) and a broad hatchet-shaped disc 
forming the body of the bone. In Lizards its 
Structure remains more complicated, resembling 
that of Birds. The body is generally simple, 
with two and sometimes three sets of cornua- 
like appendages connected with it. From the 
_ fore part of the body projects along and slender 
_ process, more or less cartilaginous, which pe- 
_ netrates the substance of the tongue. The ante- 
_ fior pair of cornua are variously folded, and the 
_ posterior placed differently in different genera; 
while the third pair, which is but seldom met 
with, seem rather to be prolongations of 
the body of the bone than separate elements 
_ appended to it. In the Chelonian Reptiles the 
_hyoid apparatus varies remarkably in form in 
different species. It generally consists of a 
central part, which is frequently itself divisible 
into several pieces, and of two or sometimes 
three pairs of cornua. Moreover, beneath the 
| anterior part of the body, there is suspended 
a bone or cartilage, which is sometimes double 
and represents the special bone of the tongue, 
which in Birds is articulated to the fore part 
_ of the body of the os hyoides. 
The os hyoides of the Crocodiles is the sim- 
 plest met with in the class of Reptiles, its 
central portion being a mere broad cartilagi- 
nous plate, convex below, concave above ; its 
" anterior part having a semicircular form, while 
_ its posterior margin is hollowed out into a con- 
| €ave edge; there are no remnants of cornua 
visible, and the os hyoides here seems to per- 
form the duties of epiglottis, hyoid, and thy- 
roid cartilage. 
_ Metamorphosis of the os hyoides.— Pro- 
_ fessor Bell having already described the most 
remarkable changes which the branchial appa- 
Tatus of the Frog undergoes during its meta~ 
‘morphosis, it would have been needless to 
Tecur to the subject again in this place, were it 
not for the purpose of collating the facts there 
‘ecorded with the series of changes we are now 
discussing, and indicating the nature of the 
‘Tespective bones delineated in a preceding 
Fig. 447. 
volume (vide Article AMpuisra, vol. i. figs. 21, 
22, 23, 24, 25, 26). Weshall, however, embrace 
the opportunity afforded of adding a few circum- 
stances to those there recorded, extracted from 
the observations of M. Martin St. Ange, con- 
nected with this most remarkable and interest- 
ing process. 
Some days before the birth of the Tadpole 
the os hyoides consists of a single median 
piece, of a pair of broad cartilaginous plates 
situated on each side of the former, anteriorly, 
and of two other similar plates occupying a 
like position behind, to each of which last are 
appended four separate styliform pieces repre- 
senting the branchial arches, making thirteen 
pieces in all. 
Examified-a little after birth, the whole car- 
tilaginous frame-work is found to have increased 
considerably in breadth, more espscially the 
eight last-mentioned cartilaginous styles upon 
which the branchial vessels run, sufficiently 
indicating their nature—moreover, they become 
united together by their distal extremities so as 
to form a series of arches, as represented in fig. 
21, vol.i. p. 98, ate. At this point of its deve- 
lopement the hyoid system of the Frog is at its 
maximum of complexity, and we will therefore 
pause to examine the elements that enter into 
its composition. The median ite (fig. 21, b, 
vol. i. p. 98) represents, according to Geoffioy, 
the glossohyat, basihyal, and urohyal elements of 
the Fish. The elements marked a will be the 
stylhyal bone, suspending the whole from the 
tympanic bone of the skull (¢ ), while the broad 
eae c, c, regarded by the same author as 
eing dismemberments of the larynx, imme- 
diately sustain the branchial arches. 
At that period, when in consequence of the 
changes that take place in the circulation of the 
Tadpole the branchial vessels are to be oblite- 
rated, the condition of the os hyoides too 
becomes rapidly changed. The cartilaginous 
arches become diminished, especially in length, 
and at last become completely absorbed except- 
ing two remnants, which are found appended to 
3H 2 
