64 SKELETON. 



and contribute to the adhesion. The periosteum is united to 

 the muscles and to the parts lying upon it, by cellular substance. 



The adhesion of the periosteum to the bones varies in the se- 

 veral periods of life. In infancy it may be separated from them 

 with great facility: in the adult it adheres more strongly in con- 

 sequence of its internal face having taken on a secretion of bone, 

 by which it is blended intimately with the bone it surrounds ; 

 and in old age it is still more adherent, from the progress of its 

 ossification. It is thick and soft in the infant, and becomes 

 ihinner and more compact as life advances. 



The organization of the periosteum is fibrous, and the fibres 

 pass very much in the same direction with the fibres of the 

 bones ; excepting the flat bones, on which it is not radiated. 

 These fibres have different lengths, the more superficial are 

 longer, while the more deeply seated extend but a small dis- 

 tance. Inflammation developes the fibres in a striking manner, 

 by occasionally making the membrane as thick as an aponeuro- 

 tic expansion. 



The blood vessels of the periosteum are numerous, and can 

 be easily injected. They come from the contiguous trunks, 

 and ramify minutely, into a vascular net-work, many of whose 

 branches penetrate into the bone, and have the distribution al- 

 ready mentioned. A few lymphatic vessels have been observed 

 in it. Its nerves have not been clearly discovered, though the 

 sensation of extreme pain, when violence is done to it in an in- 

 flamed state, may be thought a proof of their existence. In 

 health its sensations are null, or extremely obscure. 



The periosteum receives the insertion of tendons, of liga- 

 ments, and of the aponeuroses. In early life, owing to the 

 slight attachment of this membrane to the bones, all these parts 

 may be torn from them, with but comparatively little force. 

 Bichat* having advocated the opinion, that the internal laminas 

 of the periosteum become ossified in the adult, considered that 

 as a means by which all the afore-mentioned insertions into it 

 were identified with the bones. This will account for the great 

 degree of tenacity with which they adhere, and the immense 

 force they are capable of sustaining, without being detached 

 from their insertions. In this tendency to ossify, the periosteum 



* Anatomic Generale. 



