62 SKELETON. 



which penetrates by an appropriate canal, as mentioned, com- 

 monly near the centre of the bone. 



The arteries of the first two classes are generally extremely 

 small. They ramify upon the compact and cellular structure, 

 penetrating it in every direction. At death, they are common- 

 ly filled with blood, which renders the injection of them diffi- 

 cult. The third, or, as commonly called, the nutritious artery, 

 is of a magnitude proportioned to the bone to be supplied. Be- 

 ing single in every instance, it passes through the compact tis- 

 sue, and having reached the medullary cavity, it divides imme- 

 diately into two branches; each of which in diverging from its 

 fellow, goes towards its respective extremity of the bone. These 

 branches ramify into countless capillary vessels upon the mem- 

 brane containing the marrow,* and finally terminate by free 

 anastomoses with the extreme branches of the two other sys- 

 tems. 



The veins of the bones are very abundant : they are uniform- 

 ly found in company with the branches of the third, or nutri- 

 tious arteries, and their common trunk goes out at the nutri- 

 tious foramen into the general circulation. These ramifications 

 have been long known, and bring back the blood from the me- 

 dullary membrane only. The veins which receive the blood of 

 the other arteries do not attend them, and were first of all found 

 in the diploic structure of the cranium, which led to the disco- 

 very of them in all the other bones. The honour of the ori- 

 ginal observation has been claimed respectively by two very 

 distinguished men of Paris, MM. Dupuytrent and Chaussier.J 

 These veins issue from the bones by numerous openings dis- 

 tinct from those furnishing a passage to the arteries. This cir- 

 cumstance is remarkably well seen in the flat and thick bones, 

 and at the extremities of the cylindrical ones. Having left the 

 bone, they terminate, after a short course, in the common ve- 

 nous system. They arise exclusively from the spongy and com- 

 pact structure, by extremely fine arborescent branches, which, 

 uniting successively, form trunks; these trunks penetrate the 

 compact tissue, and escape from the bone by orifices which are 



* Would not this furnish a hint, that the arteries which secrete fat are diffe- 

 rent from other arteries, and that this distinction may prevail generally ? 



t Propositions sur quelques points d' Anatomic, de Physiologic, &c. Paris, 1803. 

 } Exposition de la Structure de 1'Enccphale. Paris., 1807. 



