OF THE PERIOSTEUM. 337 



The thickness of the periosteum is variable, and proportion- 

 ate to the vascularity of the bones. 



Its texture is fibrous, and fibro-cartilaginous in the places 

 where the tendons rub. It has very numerous blood vessels,* 

 and in this respect forms a remarkable exception in the liga- 

 mentous tissue. Lymphatic vessels have also been observed 

 in it, but no nerves. 



The periosteum is at first thin and has little vascularity 

 before the period of ossification. It becomes thjjik and vascu- 

 lar at this time. The use of madder does not colour it. 



The functions of the periosteum are to envelop the bones, 

 support the vessels, unite the epiphyses, in childhood, to the 

 body of the bone, and to serve at this period to insert the liga- 

 ments and tendons. 



The formation of bone has been ascribed to it, but without 

 any proof; for the ossification of the short bones is observed 

 to begin at the centre of the cartilage, and therefore far from 

 the periosteum ; and also of determining the form of the bones, 

 of limiting their growth by retaining the osseous humour, &c. 

 As to the part it may perform in the increase of the bones in 

 thickness, in the repairing the fractured bones or affected with 

 necrosis, will be examined hereafter, (chap, viii.) 



The periosteum, when divided, reunites; when it is re- 

 moved a superficial necrosis is commonly produced, and it is 

 reproduced after exfoliation. When it is inflamed, sometimes 

 is terminated by resolution, at others by gangrene ; sometimes 

 it suppurates, and then separates more or less quickly from 

 the bone, which becomes affected with necrosis ; at other times, 

 the inflammation being plastic, a deposition occurs in its thick- 

 ness, producing a periostosis, which is sometimes dispersed 

 by absorption, and at others ossifies. The periosteum is fre- 

 quently the seat of a degeneration or of a cerebriform cancer- 

 ous production, at the centre of which the bone itself is not 

 very materially altered. 



523. The perichondrium, a ligamentous membrane which 



* See Ruyscli, adv. anal, dec iii. tab. H. fig. 8. Albums, Icon, oss- foetus, 

 Tab. xvi. fig. 162. 



