THE OSSEOUS SYSTEM. 293 



this respect from the rest of the bone, and, like those of other 

 bones, such as the coracoicl and styloid processes, exhibit the 

 same disposition of the canals as that which exists in one of 

 the shorter cylindrical bones. The lamellae, fibres, and bars 

 of the spongy substance, occasionally present a few vascular 

 canals, but only when they are of some thickness. 



As the Haversian canals are vascular channels, they open 

 in certain situations : 1. externally, on the outer surface of 

 the bone ; and, 2. internally, on the walls of the medullary 

 cavities and spaces. In both situations, excessively fine and 

 coarser pores may be every where perceived, partly visible to 

 the naked eye, and which are more numerous in proportion to 

 the thickness of the cortex of the bone. But the relation of 

 the vascular canals in the compact substance to these canals 

 thus proceeding from within and without, only partially resem- 

 bles that between the branches and trunks of vessels, and only 

 in the outermost and innermost lamellae of the cortical sub- 

 stance. In the interior of the cortical portion of a bone the 

 canals are independent, and morphologically may be most 

 aptly compared to a capillary network, which at its borders 

 is in connection at many points with larger canals. A\ here 

 the cortical substance rests upon the spongy substance, as in 

 the interior of the ends of the diaphyses, and in the lateral 

 periphery of the apophyses, the vascular canals are continuous, 

 sometimes abruptly, sometimes quite gradually, expanding in 

 an infundibuliform manner, and frequently anastomosing, with 

 smaller or larger medullary spaces, so that, very often, no 

 definite limit is perceptible between them. I have never yet 

 noticed csecal terminations of the vascular canals ; it is, how- 

 ever, certain, that in many situations on the surface they must 

 constitute, over extensive spaces, closed networks, especially 

 where very few or no vessels enter the compact substance, 

 as at the points of insertion of many tendons and ligaments, and 

 beneath several muscles (temporal). 1 



1 [A most valuable contribution to our knowledge of tbe structure and develop- 

 ment of Bone has lately been made by Messrs. Tomes and De Morgan, in their 

 ' Observations on the Structure of Bone,' read before the Royal Society in June, 

 1852, but not yet published. We are enabled, however, by the kindness of those 

 gentlemen in allowing us to inspect many of their preparations, and in furnishing us 

 with the proofs of their paper, to make some very important additions and corrections 



