ON THE VERTEBRATE SKELETON. 2^1 



conditions of our globe, that not more than two pairs of the latent limbs or 

 appendages of the vertebral segments should be developed to react, as loco- 

 motive instruments, upon its waters, its' atmosphere and its dry land. 



The views of the essential relations of such limbs to the vertebrate type 

 which suggest these and similar reflections, may not be accepted by all anato- 

 mists : some may be disposed to regard the parts 62 and 04 in fig. 28 as pecu- 

 liar superadditions, rather than a reappearance of normal elements completing 

 the costal or haemal arch of a segment of the endo-skeleton and restoring it 

 to its typical condition : and, in the same spirit, they may deny the special 

 homology of the radiated appendage A, with the hinder filamentous fin of 

 the lepidosiren, and the ventral fins of other fishes, and consequently, will re- 

 pudiate its general homology as the diverging appendage of such hsemal 

 arch, and its serial homology with the simple diverging appendages of the 

 thoracic-abdominal vertebraa of fishes, crocodiles and birds. 



I am sensible how large a demand is made on the most philosophic faith in 

 general laws of organization, by seeking acquiescence in the view of the parts 

 of the hind-limb, so variously and definitely modified for special functions, as 

 having for their seat the homologues of segments and rays, which are the 

 result in the first instance of the common course of vegetative repetition of a 

 single vertebral element — an element under all circumstances compounded 

 teleogically, and, therefore, essentially one bone. 



But here I must explain what I mean by ' teleological composition.' Indi- 

 vidual parts of a skeleton, — what are commonly called ' bones,' — are fre- 

 quently ' compound ' or composed of the coalescence of several primarily 

 distinct osseous pieces. In human anatomy every single and distinct mass 

 of osseous matter entering into the composition of the adult skeleton is called 

 ' a bone' ; and Soemmerring, who includes the thirty-two teeth in his enumera- 

 tion, reckons up from 259 to 264* such bones. He counts the os spheno- 

 occipitale as a single bone, and also regards, with previous anthropotomists, 

 the os temporis, the os sacrum, and the os innominatum, as individual bones ; 

 the sternum, he says, may include two or three bones, &c*. But in' birds 

 the os occipitale is not only anchylosed to the sphenoid, but they both very 

 soon coalesce with the parietals and frontals ; and, in short, the entire cranium 

 proper consists, according to the above definition, of a single bone. Blu- 

 menbach, however, applying the human standard, describes it as composed 

 of the proper bones of the cranium consolidated, as it were, into a single 

 piecef. And in the same spirit most modern anthropotomists, influenced by 

 the comparatively late period at which the sphenoid becomes anchylosed to 

 the occipital in man, regard them as two essentially distinct bones. In direct- 

 ing our survey downwards in the mammalian scale, we speedily meet with 

 examples of persistent divisions of bones which are single in man. Thus it 

 is rare to find the basioccipital confluent with the basisphenoid in mamma- 

 lian quadrupeds ; and before we quit that class we meet with adults in some 

 of the marsupial and monotrematous species, for example, in which the supra- 

 occipital, ' pars occipitalis proprie sic dicta,' of Soemmerring, is distinct from 

 the condyloid parts, and these from the basilar or cuneiform process of the 

 os occipitis : in short, the single occipital bone in man is four bones in the 

 opossum or echidna ; and just as the human cranial bones lose their indivi- 

 duality in the bird, so do those of the marsupial lose their individuality in the 

 ordinary mammalian and human skull. In many mammals we find the 

 pterygoid processes of anthropotomy permanently distinct bones ; even in 



* De Corporis Humani Fabrica, t. i. p. 6. 



f Manual of Comparative Anatomy, by Lawrence, ed. 1827, p. 56. 



