ON THE VERTEBRATE 8KELETON. 273 
bones, in the human skeleton ; for the ossification of the thigh-bone begins at. 
four distinct points, one for the shaft, one for the head, one for the great 
trochanter, and one for the distal condyles: such deference, however, to the 
judgment of the great Comparative Anatomist has been withheld by the most 
devoted of his admirers; whose disinclination to regard these parts and pro- 
cesses as distinct bones is justified by the fact that in birds and reptiles the 
femur is developed from a single centre. 
The rule laid down by the French authorities above-cited fails in its appli- 
cation to the difficult question of the nature and number of bones in a skeleton, 
because they did not distinguish between those centres of ossification that 
have homological relations, and those that have only teleological ones ; 2. e. 
between the separate points of ossification of a human bone which typify 
vertebral elements, often permanently distinct bones in the lower animals; and 
the separate points which, without such signification, facilitate the progress 
of osteogeny and have for their obvious final cause the well-being of the grow- 
ing animal. The young lamb or foal, for example, can stand on its four legs as 
soon as it is born; it uplifts its body from the ground and soon begins to 
run and bound along. The shock to the limbs themselves is broken and 
diminished at this tender age, by the divisions of the long bones, and by the 
interposition of the cushions of cartilage between the diaphyses and epiphy- 
ses. And the jar that might affect the pulpy and largely developed brain of 
the immature mammal, is further diffused and intercepted by the epiphysial 
articular extremities of the bodies of the vertebre. 
We thus readily discern a final purpose in the distinct centres of ossifica- 
tion of the vertebral bodies and the long bones of the limbs of mammals 
which would not apply to the condition of the crawling reptiles. The dini- 
nutive brain in these low and slow cold-blooded animals does not demand 
such protection against concussion; neither does the mode of locomotion in 
the quadruped reptiles render such concussion likely : their limbs sprawl out- 
wards and push along the body which commonly sweeps the ground; there- 
fore we find no epiphyses at the ends of a distinct shaft in the long bones 
of saurians and tortoises. But when the reptile moves by leaps, then the 
principle of ossifying the long bone by distinct centres again prevails, and the 
extremities of the humeri and femora long remain epiphyses in the frog. 
' . A final purpose is no doubt, also, subserved in most of the separate centres 
of ossification which relate homologically to permanently distinct bones in 
the general vertebrate series ; it has long been recognised in relation to faci- 
litating birth in the human fcetus; but some facts will occur to the osteo- 
genist, of which the teleological explanation is by no means obvious. 
» One sees not, for example, why the process of the scapula which gives at- 
tachment to the pectoralis minor, the coraco-brachialis, and the short head of 
the biceps should not be developed by continuous ossification from the body 
of the blade-bone, like that which forms the spinous process of the same 
bone. It is a well-known fact, however, that not only in man, but in all mam- 
mals, the coracoid process is ossified from a separate centre. In the mono- 
tremes it is not only autogenous, but is as large a bone as in birds and reptiles, 
in which it continues a distinct bone throughout life. Here, then, we have 
the homological, without a teleological explanation of the separate centre for 
the coracoid process in the ossification of the human blade-bone. 
This distinction in the nature and relations of such centres is indispen- 
sable in the right application of the facts of osteogeny to the determination 
_ of the number of essentially distinct bones in any given skeleton. 
7 
_ All those bones which consist of a coalescence of parts answering to di- 
stinct elements of the typical vertebra are ‘homologically compound.’ 
