648 



SKELETON. 



While clavicles, coracoid bones, and ribs 

 appear identical, we then can readily under- 

 stand how a bird or reptile may possess two 

 or more clavicles, according as the laws of 

 form shall subject two or more of the original 

 costae to clavicular modification. The cla- 

 vicles, therefore, of the mammal and the cla- 

 vicles and coracoids of the bird or reptile 

 being costal quantities under metamorphosis, 

 these bodies are to be regarded as the ribs 

 proper to those cervical vertebrae, opposite to 

 which they appear in all skeletal forms.* 



PROP. XXXV. Marsupial bones, pubic and 

 ischiadic bones, and ribs, are identical parts of 

 the costo-vertebral whole quantities or archetypes. 

 Wherever we find these parts, viz. sternum, 

 rib, and vertebral piece, occurring in skeletal 

 fabrics, we shall never find that they take the 

 place of each other. The sternum, even when 

 appearing isolated from the other parts, is still 

 holding its proper locality at the median line 

 in front. The rib is always found laterally, 

 and the vertebral piece always behind. The 

 sternal pieces hold serial order, and hence we 

 know them throughout all variety of modifi- 

 cation. The costae in like manner hold serial 

 order, and hence we also recognise these parts. 

 The vertebral pieces hold their own serial 

 order, and thus we know them. The costal, 

 the sternal, and the vertebral serial orders 

 are never interrupted by the introduction of a 

 new and unknown element among the bodies 

 which form each serial line. There never 

 occurs among the vertebral pieces behind any 

 other thing which by being difform to vertebrae, 

 may disconnect that vertebral series. The 

 same remarks apply to the sternal bodies in 

 front, and the same to the costal pieces ar- 

 ranged laterally. Every body which holds 

 serial order with the sternal bone is a sternal 

 bone, and constituting sternal serial order. 

 Every body which holds serial order with a 

 vertebral bone is a vertebral bone, and consti- 

 tuting vertebral order. Every body, also, 

 which takes serial order with a rib is a rib, 

 and constitutes costal-serial order. Every 

 body, therefore, which on first sight shall seem 

 to be specifically distinct from that order with 

 which it holds series, is in fact only rendered 

 special in such order by modification ; origin- 

 ally it is identical with all the pieces of that 

 same order. 



Just as the clavicle and coracoid bone hold 

 series with ribs, and are ribs originally, but 

 rendered special by modification, so does it 

 appear that the marsupial, the pubic, and is- 

 chiadic bones, which hold serial order with 

 ribs are ribs originally, but now presenting in 

 such conditions of modification as we mark by 



* The same reasoning which leads the author of 

 the " Homologies " to refer the coraco-scapular arch 

 to the occipital vertebra, induces him to pronounce 

 the mammal clavicle to be naturally related to the 

 atlas vertebra. Now, I cannot understand why the 

 author's views, which are certainly correct, in so far 

 ns he is led to believe the pair of clavicles to be the 

 inferior arch of some one of the cervical vertebras, 

 should make choice of the atlas so remote, in prefer- 

 ence to that cervical vertebra, opposite which the 

 clavicles appear. 



nomenclateric difference. A clavicle, a cora 

 coid bone, a marsupial bone, a pubic bone, and 

 an ischiadic bone, are thus differently named 

 in order to point to their several specialities of 

 caste. But through these special characters 

 their costiform original character is still visible, 

 and therefore I call them ribs modified. These 

 modifications which clavicles, coracoids, mar- 

 supial, pubic, and ischiadic bones present, 

 when contrasted with each other and with 

 ribs, are in reality of no greater amount than 

 those varieties which are apparent among those 

 bodies which we name ribs, enduring as such 

 through the skeletal axis. At the present 

 day we well know that the thing named rib is 

 not necessarily confined to that region of the 

 skeletal axis named thorax. Ribs are found 

 embracing the ventral region of fishes, and all 

 spinal regions of ophidians. Ribs of unequi- 

 vocal character are also developed embracing 

 the venter of Saurians. Ribs are jutting out 

 laterally from the loins of the draco volans, 

 supporting the parachute of that animal. In 

 fact we can readily distinguish the costal cha- 

 racter of many bones, even though they are 

 separated from their proper vertebral centres 

 behind. See these osseous quantities, which 

 project from the sternal bone behind, ensheath- 

 ing the venter of the bird's, and the Saurian's 

 skeleton, and standing free from the lumbar 

 vertebral pieces, to which, nevertheless, they 

 refer, are they not ribs, which special laws 

 have dissevered from the spinal axis behind ? 

 It is not, therefore, necessary to the bone 

 named costa, that it should always hold at- 

 tached to the vertebral form posteriorly, and 

 to the sternal form anteriorly. And why, 

 therefore, not extend the name costa to those 



Fig. 473. 



osseous parts which do not present greater 

 varieties compared to ribs, than ribs do when 

 compared to each other. .The law of serial 



