THE OSSEOUS SYSTEM. 



327 



osseous substance derived from the cartilage and periosteum of the 

 younger bones ; in this case the first three, E E, E 1 E 1 , and E 2 E 2 . 



In the cylindrical bones, without a 

 medullary cavity, and in all other bones 

 containing nothing but spongy substance 

 in the interior, the absoprtion does not 

 proceed to nearly the same extent as it 

 does in the above described cases, that is 

 to say, only to the production of a looser 

 spongy substance in the interior, and, 

 consequently, we find, for instance in the 

 vertebrae, more or less considerable re- 

 mains even of the earlier bone-substance. 

 In this situation also, the absorption al- 

 ways affects not merely the osseous nu- 

 cleus, formed from the cartilage, but like- 

 wise the periosteal layers, the latest of 

 which only remain more in their original 

 form, as the substantia compacta. 



The Haversian canals do not originate, 

 as is sufficiently apparent from what has 

 been said, like the cancelli of the primary 

 bone-substance, from a solution of a pre- 

 existing tissue, but are nothing more than 

 open cavities, left from the commence- 

 ment, in the periosteal layers. They are 

 relatively, of a considerable size at an 

 early period (vid. also "Valentin. Entw." 

 p. 262), measuring in the foetal humerus 

 at five months 0-016-0-024 of a line in 

 the femur at birth, according to Harting 



(p. 78), 0*10-0-024 of a line, just as in the most recently formed layers 

 also of a later period. Their contents have been already described. The 

 most important circumstance connected with them remaining to be no- 

 ticed, is the mode in which their lamellar systems originate. These 

 lamellse also are formed without the intervention of cartilage, and are 

 nothing more than deposits from the contents of the canals, which sub- 

 Fig. 134. Diagram of the growth of a cylindrical bone. JB, primary rudiment, the dia- 

 physis ossified and the epiphyses cartilaginous: .4, the same bone in four stages of further 

 advance, E'PPE 1 , E^P'E 2 , E 3 P 2 P 2 E 3 , E 4 F 3 P 3 E 4 ; P P'P 2 P 3 , periosteal layers of these four 

 bones; the space contained within 1, 2, 3, 4, and I 1 , 2 1 , 3 1 , 4 1 , indicates the portion which 

 in the largest bones is formed from cartilage ; E'E', cartilaginous epiphyses of the second 

 bone; E 2 E 2 , epiphyses of the third bone, in one of which is an osseous nucleus ; E 3 E 3 , E 4 

 E 4 , epiphyses of the fourth and fifth bones, all with larger epiphysal nuclei: G, articular 

 cartilage ; I, K, interstitial cartilage between the ossified epiphyses and diaphyses. 



