822 



OSSEOUS SYSTEM. (CoMp. ANAT.) 



further advance of ossification at any assignable 

 point of developement, leaving some parts per- 

 manently atrophied, 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 be a 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 

 person who is only acquainted with the osteo- 

 logy 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 



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 instruments 

 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 pointed out, let us now proceed briefly 

 to glance at the parts of which it would consist, 

 and these we should find to be the following. 



Fig. 432. 



s 







* Vide a Memoir on the structure of this extra- 

 ordinary production of nature, by John Goodsir, Esq. 



Skeleton f>f the Crocodile. 



