J 06 LOCOMOTION. [CHAP. v. 



larity of the subject. In the female, for instance, they are less dis- 

 tinct than in the male ; in the powerfully muscular man they are 

 at the maximum of development. As Sir Charles Bell has re- 

 marked, a person of feeble texture and indolent habits has the bone 

 smooth, thin, and light ; while with the powerful muscular frame is 

 combined a dense and perfect texture of bone, where every spine 

 and tubercle are well developed. And thus the inert and mechanical 

 provisions of the bone always bear relation to the muscular power 

 of the limb; and exercise is as necessary to the perfect constitution 

 of a bone, as it is to the perfection of muscle. It is an interesting 

 fact, that if a limb be disused, from paralysis, the bones waste as 

 well as the muscles. 



Of the Vessels of Bone. We now proceed to inquire into the 

 manner in which the nutrition of bone is provided for. A texture 

 containing so much animal matter, and needing a constant supply of 

 inorganic material likewise, must necessarily be largely supplied 

 with blood, the common source of the materials of all the tissues. 



The blood-vessels of bone are very numerous, as may be satis- 

 factorily seen on examining a well-injected specimen. The arteries 

 are in great part continued from those of the periosteum : those 

 which penetrate the cancellated texture of the extremities of the 

 long bones are very large, and ramify freely among the cancelli. 



The membrane of the medulla which is contained in the shaft, 

 receives its blood from a special artery that pierces the compact 

 tissue through a distinct canal, known as that for the nutritious 

 artery. This vessel divides into two immediately on entering the 

 medullary canal; of these, one ascends, the other descends, and 

 both break up into a capillary network, anastomosing with the 

 plexuses in the extremities of the bone, derived from the arteries 

 that penetrate there. From the copious vascular network thus 

 formed within the bone, the innermost part of the compact sub- 

 stance of the shaft receives its blood-vessels. 



In the compact tissue the arteries pass into very narrow capillary 

 canals, most of which are invisible to the naked eye. In carefully 

 raising the periosteum from a bone that has been subjected to a 

 little maceration, the vessels maybe seen in great numbers passing 

 from that membrane into the osseous texture, and many of the 

 larger ones seem to be surrounded by a sheath derived from the 

 periosteum. Similar sheaths may be seen surrounding the vessels 

 of the cancellated texture. 



The vascular canals of the compact tissue are styled Haversian, 

 after their discoverer, Clopton Havers. They are disseminated 



