eii BONE. 



central cavity and the adjoining Haversian canals. Its ramifications anas- 

 tomose with the arteries of the compact and cancellated structure ; indeed, 

 there is a free communication between the finest branches of all the vessels 

 which proceed to the bone, and there is no strictly defined limit between 

 the parts supplied by each. In the thigh-bone there are two medullary 

 arteries entering at different points. 



The veins of the cancellated texture are peculiar and deserve special 

 notice. They are large and numerous, and run separately from the arteries. 

 Their arrangement is best known in the bones of the skull, where, being 

 lodged in the diploe or spongy texture between the outer and inner compact 

 tables, they have received the name of the diploic veins. They run in 

 canals formed in the cancellated structure, the sides of which are con- 

 structed of a thin lamella of bone, perforated here and there for the admis- 

 sion of branches from among the adjoining caucelli. The veins, being thus 

 inclosed and supported by the hard structure, have exceedingly thin coats. 

 They issue from the bone by special apertures of large size. A similar 

 arrangement is seen in the bodies of the vertebrae, from whence the veins 

 come out by large openings on the posterior surface. 



The lymphatics of the bones are but little known ; still, there is evidence 

 of their existence, for, independently of the authority of Mascagni (which 

 is of less value in this particular instance, inasmuch as he does not state 

 expressly that he injected the vessels which he took for the lymphatics of 

 bone), we have the testimony of Cruikshank, who injected lymphatics 

 coming out of the body of one of the dorsal vertebrae, in the substance of 

 which he also saw them ramifying.* 



Fine nerves have been seen passing into the medullary canal of some of 

 the long bones along with the artery, and following its ramifications, but 

 their ultimate distribution is doubtful ; and Kolliker describes fine nervous 

 filaments as entering with the other arteries of the bone to the spongy and 

 compact tissue. As far, however, as can be judged from observations on 

 man and experiments on the lower animals, the bones, as well as their 

 investing periosteum, are scarcely if at all sensible in the healthy condition, 

 although they are painfully so when inflamed. 



Some hold that the same is true of the marrow, or rather the medullary membrane ; 

 others, among whom are Duverney and Bichat, affirm, on the contrary, that the 

 medullary tissue is sensible. They state that, on sawing through the bone of a living 

 animal, and irritating the medullary membrane by passing a probe up the cavity, or 

 by injecting an acrid fluid, very unequivocal signs of pain will be manifested. 

 Beclard, who affirms the same fact, points out a circumstance which may so far 

 account for the result occasionally turning out differently, namely, that when the 

 bone happens to be sawn through above the entrance of the medullary artery, the 

 nerves going along with that vessel are divided, and the marrow consequently ren- 

 dered insensible, as happens with any other sensible part when its nerves are cut. 



Formation and grou'th of bone. The foundation of the skeleton is laid at 

 a very early period ; for, among the parts that appear soonest in the embryo, 

 we distinguish the rudiments of the vertebrae and base of the skull, which 

 afterwards form the great median column to which the other parts of the 

 bony fabric are appended. But it is by their outward form and situation 

 only, that the parts representing the future bones are then to be recognised ; 

 for at that early period they do not differ materially in substance from the 

 other structures of the embryo, being, like these, made up of granular 



* Anatomy of the Absorbing Vessels, 1790, p. 198. 



