ON THE VERTEBRATE SKELETON. 271 
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 64 in fig. 28 as pecu- 
liar superadditions, rather than a reappearance of normal elements completing 
the costal or hemal 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 hemal 
arch, and its serial homology with the simple diverging appendages of the 
thoracic-abdominal vertebra of fishes, crocodiles and birds. 
Tam 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 ne Indi- 
vidual —— of a skeleton,—what are commonly “called < bones,’—are fre- 
quently ‘ compound’ or composed vf 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 innomiratum, 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 asingle 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 
piecet. 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 sccipitis: in short, the single occipital bone in wan is four bones in the 
opossum or echidna ; and just as the human cranial bones lose their indivis 
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 
SUPT * De Corporis Humani Fabrica, t. i. p. 6. 
+ Manual of Comparative Anatomy, by Lawrence, ed. 1827, p. 56. 
