834 
of their life a true branchial apparatus, which 
subsequently becomes absorbed to give place 
to thoracic or pulmonary respiration, and 
consequently they are furnished in the first 
portion of their existence with the hyoid 
system of a fish, which, passing through dif- 
ferent phases of gradually diminishing com- 
lexity, is slowly converted into the simple 
orm it presents in their mature or adult 
condition. So diversified, in fact, is this por- 
tion of the osseous skeleton in the different 
classes of Vertebrata, that the anatomist only 
acquainted with human osteology would never 
~be able to recognise the analogy between what 
he sees in man and the condition in which it 
exists in its more complicated states, or at all 
understand the metamorphosis which it un- 
dergoes in the embryo of Mammalia, without 
tracing it through all its forms, as we shall 
now proceed to do with as much brevity as is 
compatible with our subject. 
In the Fish the os hyoides is situated as in 
_all the other Vertebrata, and is composed of 
twelve bones. It consists of two branches, 
each made up of five distinct elements, namely, 
the styloid bone (29), which suspends it to the 
temporal; two broad lateral pieces (fig. 436, 
37 and 38) placed one behind the other, and 
two small bones (39 and 40) placed one above 
the other at the anterior extremity of each 
branch, and forming with their fellows of the 
opposite side a kind of symphysis uniting the 
two halves of the bone. In front of this sym- 
physis is a single bone, the lingual (41) situ- 
ated as in Birds and Reptiles, and behind in 
the angle formed by the union of the two 
branches another azygos piece representing the 
tail of the os hyoides so distinct in Lizards and 
in Birds. This latter piece becoming joined to 
the symphysis of the Scant bones forms the 
isthmus that inferiorly separates the two bran- 
chial apertures of the fish. 
Appended to the inferior and external mar- 
gin of each branch of the os hyoides of a fish, 
are the branchiostegous rays (fig. 437, 43), 
destined to support the branchiostegous mem- 
brane that completes the gill-covers. These 
are very various both in number and form in 
different fishes; they are fixed to the os hy- 
oides by distinct articulations, sometimes by 
simple ligaments. Autenrieth and Geoffroy 
suppose these branchiostegous rays to be the 
representatives of sternal ribs, but doubtless 
they belong rather to the exo-skeleton. 
0 facilitate, however, a comparison between 
the above complicated series of bones and the 
corresponding pieces met with in other classes, 
it will be advisable to lay before the reader the 
result of the elaborate analysis of this part of 
‘the skeleton made by Geoffroy St. Hilaire, 
whose names applied to the various elements 
composing it are not only classically elegant, 
but from their simplicity will save much useless 
circumlocution. When complete, the distin- 
guished anatomist alluded to considers the 
os hyoides to consist of the following parts: 
The body or basihyal piece, forming the central 
portion of the fabric; the urohyal or tail of 
the os hyoides (fig. 437, 42); the entohyal, 
OSSEOUS SYSTEM. (Comp. Anat.) 
a piece sometimes int between the two 
former; two glossohyals or posterior cornua 5 
two apuhyals (39) forming the first pieces of the 
anterior or styloid cornua; two ceratohyals(40) 
forming the second pieces of these 3 
and lastly, two stylohyals (29), which are re~ 
presented in the human subject by the styloid 
rocesses of the temporal Lie a oa 
Appended to this hyoid apparatus are a 
ledias' of lateral arches a alatien in their im- 
portance the ribs in the water-breathing Ver- — 
tebrata, and indeed somewhat resembling them — 
in structure and arrangement, along which run 
the branchial vessels to the gills, and subse- 
quently from the gills to form the aorta. These 
arches have in Sct, by soe continental an ato 
mists, been actually loo upon as repre-— 
senting the thorax of Vertebrata that respire 
the air, but with little reason, as must be evi- 
dent on considering how, as the real thorax is 
called into play, these are gradually absorbed 
and disappear. ee. 
The branchial arches of a fish, from which 
are suspended the branchial fringes, consist om 
each side of four chains of bones adherent by 
their inferior extremities to an intermedi te 
series of ossicles, which is connected ante- 
riorly with the symphysis of the os hyoide 
between the four anterior elements of that bo 
and above its ¢ail. Superiorly the_bravichiz 
arches are fixed by a ligamentous attachmen 
beneath the cranium. 
The series of intermediate bones with whiel 
the pairs of branchial arches are connected | 
feriorly, are placed behind the lingual and ar 
three in number, forming a kind of little ste 
num to the hyoid apparatus. 
branchial arches consists of a superior and i 
ferior portion that are moveable upon eai 
other. The inferior portion (, Sig. 437, 58) 
that connected with the intermediate chat 
bones, and in the anterior three pairs of are 
this is formed of two pees t 
ir has this part composed of only one pi 
The upper Seine of the branchial ar 
are made up of a single bone. The tht 
posterior (fig. 437, 61) support the phar 
geal bones (fig. 437, 62), while the anteric 
attached to the skull by the intervention 
little style (59), which might be regardet 
the pharyngeal bone belonging to this pair. 
Internally all the branchial arches are 
vided with osseous plates or ridges whic 
generally covered with teeth. per 
in some degree the function of the epi 
of Mammalia, inasmuch as they p even 
thing taken into the mouth from getting 
the gills along with the water as it passes 
respiratory organs. ma 
e pharyngeal bones are iar to 
and .. ainated in the dueat: whe 
powerfully assist in masticating the food 
are usually two inferior and six superior, 
inferior (fig. 437, 56) are attached behi 
branchie in the angle formed by the i 
of branchial arches; they are generally 
triangular shape, and form a kind of fi 
the pharynx. The upper pieces (figs 
62) are three in number on each side, 
