822 
further advance of ossification at any assignable 
point of developement, leaving some parts per- 
manently — ied, while others are allowed 
to attain their full growth, we find great varieties 
in the composition of the osseous framework. The 
Tadpole, were its growth arrested before its limbs 
begin to sprout, would bea Fish. The Frog, if it 
ceased to grow when its limbs were but par- 
tially formed, would be a Siren or a Proteus, 
having little or nothing in common with the 
adult creature as regards the configuration or 
even the number of the bones in its skeleton. 
Which of the three conditions must the com- 
parative anatomist refer to in order to estimate 
the condition of the bones composing the frame- 
work of this Batrachian? The importance of 
this inquiry will be at once obvious, as, either 
in the first instance there must have been a 
much greater number of bones developed than 
are met with in what is usually considered a 
complete skeleton, or in the adult animal the 
bones have become too much confused with 
each other to allow us at all to estimate their 
real condition. It is sufficient indeed for any 
rson who is only acquainted with the osteo- 
ogy of man, to cast his eyes over the bones 
entering into the composition of the skeleton 
of a fish to perceive at once that the nomen- 
clature employed by the human anatomist is 
by no means sufficiently ample to afford names 
to one-half of them, which indeed have no re- 
presentatives in the human body; or even the 
bare comparison of the adult human cranium 
with that of the infant of tender age would 
convince us that in the former there are many 
more distinct bones than in the latter. The 
only mode of solving these difficulties is ob- 
viously to study the composition of every part 
of the skeleton in the most complicated form 
under which it is met with, and having ascer- 
certained the number and disposition of the 
pieces of which it then consists, and settled 
the names and analogies of each, it becomes 
comparatively easy to point out what parts are 
deficient in less complex forms of the ske- 
leton. 
The number of pieces which can normally 
enter into the construction of any portion of 
the osseous apparatus having been thus deter- 
mined, these are regarded as the primary ele- 
ments of the skeleton, by the developement, 
suppression, enlargement, or modified form of 
which every required variety of the bony 
framework may be explained, and the con- 
struction of this portion of the animal economy 
proved to be in accordance with certain immu- 
table laws that may be traced throughout the 
immense series both of the existing and of 
extinct races of Vertebrata. 
It will readily be perceived after the above 
remarks that a perfect skeleton, that is, a skele- 
ton presenting all the parts of which it might 
normally be composed in a complete state of 
developement, does not exist in nature. 
A spinal column may exist alone without 
either cranium, face, or limbs, as is the case in 
that strange and rare fish the Amphioxus.* Or 
* Vide a Memoir on the structure of this extra- 
ordinary production of nature, by John Goodsir, Esq. 
OSSEOUS SYSTEM. (Compr. Anat.) 
the spine, cranium, face, and extremities may — 
coexist without ribs or thorax, as in the Frog. 
The spine and cranium form almost the entire 
skeleton of many apodal Fishes, while in Ser-— 
pents the ribs become the chief instraments 
employed in locomotion, not even vestiges of 
legs or arms being visible. = 
Imagining, however, that a fully formed ske- 
leton, having every apparatus belonging to it, 
could be potnted eat leu us now orocbal briefl; 
to glance at the parts of which it would consist, 
eth these we should find to be the following. — 
‘ig. 432. 
oy 
LARAA ADS 
a i (eee 
* 
Skeleton of the Crocodile. 
