- VESSELS AND SERVES OF BOXE. 93 



in the compact substance. These arc both arterial and renons, but 

 according to Todd and Bowman, the two kinds of vessels occuj^y 

 distinct passages ; and the veins, which are the larger, are said to 

 present, at irregular intervals, pouch-like dilatations. Arteries, of larger 

 size but fewer in number, proceed to the cancellated texture. In the 

 long bones numerous apertures may be seen at the ends, near the 

 articular surfaces ; some of these give passage to the arteries referred 

 to, but the greater number, as well as the larger of them, are for the 

 veins of the cancellated texture, which run separately from the arteries. 

 Lastly, a considerable artery goes to the marrow in the central part of 

 the bone ; in the long bones this medullary artery, often, but impro- 

 perly, called " the nutritious artery," passes into the medullary canal, 

 near the middle of the shaft, by a hole running obliquely through the 

 compact substance. The vessel, which is accompanied by one or two 

 veins, then sends branches upwards and downwards to the marrow and 

 medullary membrane in the central cavity and the adjoining Haversian 

 canals ; from these branches capillaries pass radially towards the peri- 

 phery. The comparatively narrow arterial capillaries pass suddenly into 

 the wide venous ones, so that the current of blood must be considerably 

 retarded both in these and in the large thin-walled veins. The blood con- 

 tained in these is said to possess a large number of pale corpuscles, as 

 ■well as transitions from these to the red. The ramifications of the me- 

 dullary artery anastomose with the arteries of the compact and cancel- 

 lated 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 structm-e, the 

 sides of which are constructed of a thin lamella of bone, perforated 

 here and there for the admission of branches from the adjoining 

 cancelli. 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 vertebras, from w'hence 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 Mas- 

 cagni (who, however, does not state 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 veftebrK, in the substance of which he also saw them 

 ramifying."' The lymphatics in the periosteum have been already 

 noticed (p. 91). 



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 Kulliker describes fine 



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



