ON THE VERTEBRATE SKELETON. 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 ; i. 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 vertebrae. 



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 dimi- 

 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 foetus ; 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. 



All those bones which consist of a coalescence of parts answering to di- 

 stinct elements of the typical vertebra are ' homologically compound.' 



