STRUCTURE OF BONE. 335 



§ 3. Formation and Deielopement of Bone. 



But it is not enough to contemplate the purposes 

 so admirably answered by these arrangements. Our 

 curiosity cannot but be powerfully excited to learn 

 what processes and refined series of means are 

 employed by nature to raise and to perfect all 

 these artificially contrived structures. It fortu- 

 nately happens that in this instance we are per- 

 mitted to penetrate a little farther than usual into 

 the secrets of organic evolution : for the succession 

 of changes can be better followed by the eye in 

 the slow developement of the harder parts, than in 

 the quicker growth of more yielding and expansible 

 textures. The peculiar material, also, of which 

 bone is formed, is easily distinguished by its hard- 

 ness, its whiteness, and its opacity from the softer 

 and more transparent animal substance with which 

 it is intermixed. Hence we are allowed an oppor- 

 tunity of observing the earliest stages of its deposi- 

 tion, and of accurately following the subsequent 

 changes it undergoes. 



The parts of the embryo animal, w^hich are des- 

 tined to become bone, partake of the soft and 

 gelatinous consistence, which, at that early period, 

 characterizes all the textures of the body ; and 

 they can hardly, indeed, be distinguished from the 

 semi-fluid portions which surround them. In pro- 

 cess of time, when the vascular circulation of the 

 blood has been established, and the newly formed 

 vessels are extending their branches over every 

 part of the nascent organization, the arteries which 



