OF THE PERIOSTEUM. 63 



uniformly smaller than the bony canals, of which they are the 

 terminations. The canals are formed of compact substance, 

 continued from the external surface of the bone, and are lined 

 by the contained veins. The parietes of the canals are pene- 

 trated by smaller veins entering into the larger. M. Dupuy- 

 tren is of opinion, that only the internal membrane of the ve- 

 nous system exists in this set of veins; that it. adheres closely to 

 the bone, so as to be incapable of exerting any action upon the 

 blood ; that it is very thin, weak, transparent, and is thrown 

 into numerous valves. 



Lymphatic vessels are generally seen only on the surface of 

 the bones. Mr. Cruikshank, however, on one occasion, while 

 injecting the intercostal lymphatics, passed his mercury into the 

 absorbents of a vertebra, and afterwards saw them ramifying 

 through its substance;* a fact which, along with what is known 

 of the power of exfoliation in bones, proves sufficisntly the ex- 

 istence of such vessels in them. Nerves have also been traced 

 into them, accompanying the nutritious arteries.t 



CHAPTER IL 



SECT. I. OF THE PERIOSTEUM. 



THE membrane which surrounds the bones is called perios- 

 teum, and is extended over their whole surface, excepting that 

 covered by the articular cartilages. As this membrane ap- 

 proaches the extremities of the bones, it is blended with the li- 

 gaments uniting them to each other, from which the ancients 

 adopted the opinion, that the ligaments and periosteum were 

 the same. Many fibres pass from the periosteum to the bone, 

 by which it is caused to adhere. These fibres are more nume- 

 rous and stronger at the extremities than in the middle of the 

 cylindrical bones ; also upon the thick bones, than upon the flat 

 ones. The blood vessels of the bones accompany these fibres 



* Anatomy of Absorbing Vessels, p. 98. London, 1790. 

 f Beclard, Elemens d'Anatomie Generale. Paris, 1823. 



