THE OSSEOUS SYSTEM. 333 



All the vessels of bone, — the medullary vessels of the apophyses 

 and of the diaphyses, as well as the vessels of the compact 

 substance, — communicate in a multiplicity of ways, so that the 

 vascular system throughout the entire bone constitutes a con- 

 tinuous whole, in which it is possible for the blood from any 

 one part to reach every other part ; for it was observed by 

 Bichat (' Anat. General./ 1812, III, p. 37), in an injected 

 tibia, the nutritious artery of which was obliterated, that the 

 bifurcation of the vessel in the medullary canal was well 

 injected, and that the nutrition of the marrow was evidently 

 unaffected. 



In the short bones, the blood-vessels present pretty nearly 

 the same conditions as they do in the apophyses of the long 

 bones ; the arteries and veins of larger and smaller size enter- 

 ing and quitting the bone at numerous points on the surface, 

 and sometimes, as in the posterior aspect of the bodies of the 

 vertebrae, in very large trunks, — the venae basi-vertebrales of 

 Breschet, furnishing a capillary plexus to the medulla, and also 

 penetrating into the few Haversian canals of these bones. 



In the flat bones, such as the scapula and os innominatum, 

 there are distinct nutritious foramina for the larger arteries 

 and veins; the compact substance receiving finer vessels from 

 the periosteum, and the spongy substance being supplied by 

 numerous and even large vessels, as in the neighbourhood of 

 the articular cavities. In the flat cranial bones, the arteries, 

 for the most part, enter both the cortical and spongy substance 

 from without, on both surfaces, presenting the usual conditions, 

 whilst the vena diploeticce, as they are termed, have only their 

 extremities free in the medulla, as in other bones, their 

 trunks, and larger and smaller branches running indepen- 

 dently and generally unassociated with medullary substance 

 in large, arborescent, special channels, the so-termed "canals 

 of Breschet," which open at determinate points with large 

 apertures {emissaria Santorini), and communicate freely with 

 the veins of the dura mater, with respect to which relations, 

 however, works on special anatomy must be consulted. The 

 size and number of the veins in the cranial bones, is, moreover, 

 extremely variable, and they are constantly becoming obli- 

 terated, particularly in old age, concomitantly with the frequent 

 diminution of the diploe, on which account also the venous 



