1*72 DEVELOPMENT OP BONK 



fused into one solid bone, till, according to the observa- 

 tions made, the individual has advanced to the sixteenth 

 or eighteenth year of age, or even till later in life. 



Ossification of the flat bones takes place between mem- 

 branes, but, nevertheless, in cartilage also, which, however, 

 is so small in quantity as to lead some to deny its existence. 

 The point where the bony matter is first deposited depends 

 on the bone being either single or compound in its nature. 

 The parietal has one point of ossification, the frontal two, 

 and the occipital several, from which points the osseous 

 fibres radiate in every direction, till, at the period of birth, 

 we have the whole bony casement for the head complete, 

 excepting the fontanelles, which are not closed till the third 

 year after birth. 



The thick bones have one or more points of ossifica- 

 tion, according as they are either single or double. The 

 carpus and tarsus present specimens of the former variety, 

 while the bones of the vertebra? furnish examples of the 

 latter. 



There yet remains great obscurity in regard to the pre- 

 cise manner in which cartilage is changed or becomes bone. 

 The microscope shows cartilage to contain, or, as Von Behr 

 expresses it, consist of a mass of homogeneous cells, carti- 

 lage cells, in the centre of which the medullary canaliculi 

 or Haversian canals are formed, surrounded by capillary 

 vessels. In the parietes of these canals and in the lamellae, 

 the lacunas or corpuscles and the calcigerous tubes appear, 

 after which the deposit of osseous matter seems to take place. 

 The cartilage cells are regarded as the basis of this change. 

 Ossification does not commence at the same time in all the 

 bones. At the end of the first month the clavicle and lower 

 jaw are found to be partly ossified; at the end of the second, 

 the bodies of the long bones, the ribs, vertebras, base of the 

 skull, and pelvis have commenced ossifying; and from this 

 time to that of birth, there are only a few in which ossifica- 

 tion has not begun, such as the patella? and a few bones of 

 the tarsus and carpus. The ossific process is much more 

 rapid in some bones than others, and in some parts of the 



