BOXE. ci 



tebrse, and sternum, and in variable number in the scapula, the innominate, and 

 facial bones. 



The marrow serves the same general purposes in the economy as ordinary fat. 

 Placed within the bones, which are made hollow for the sake of lightness, it serves as 

 a light and soft material to fill up their cavities and support their vessels. In birds, 

 for the sake of still further lightening their skeleton, the larger bones, instead of 

 being filled with marrow, contain air, which passes into them from the lungs by 

 openings at their extremities. Even in man there are certain hollow bones of the 

 cranium and face which are naturally filled with air. The cavities of these bones are 

 named sinuses; they open into the adjoining air-passages, and are lined with a 

 prolongation of the mucous membrane, underneath which is a thin periosteum, " 



The bones do not at first contain fatty marrow ; in the foetus their cavities are 

 filled with a transparent reddish fluid, like bloody serum, only more consistent and 

 tenacious, with granular marrow-cells. In dropsical subjects also, the marrow, like 

 the rest of the fat, is consumed to a greater or less extent, its place being occupied by 

 a serous fluid. 



Blood-vessds. The bones are well supplied with blood-vessels. A net- 

 work of periosteal vessels covers their outward surface ; others penetrate to 

 the cavities of the spongy part and the medullary canal, on the sides of 

 which they ramify ; and fine vessels, deprived of their muscular coat, run 

 through all parts of the compact tissue in the Haversian canals. The sides 

 of these internal cavities and canals make up together a large extent of 

 inward surface on which vessels are srread. The nutritious fluid conveyed 

 by these vessels no doubt escapes through their coats and permeates the 

 surrounding dense bone interposed between the vascular canals ; and it 

 seems highly probable that the system of lacunas and communicating canali- 

 culi, already described, is a provision for conducting the exuded fluid 

 through the hard mass. When a bone is macerated, its vessels and mem- 

 branes are destroyed, whilst the intermediate true bony matter, being of an 

 incorruptible and persistent nature, remains ; a process which, for obvious 

 reasons, cannot be effected with the soft tissues of the body. 



The vessels of bone may be recognised while it is yet fresh by the colour 

 of the blood contydued in them ; but they are rendered much more con- 

 spicuous by injecting a limb with size and vermilion, depriving the bones 

 of their earth by means of an acid, and then drying them and putting them 

 into oil of turpentine, by which process the osseous tissue is rendered trans- 

 parent whilst the injected matter in the vessels retains its red colour and 

 opacity. Numberless small vessels derived from the periosteum, as already 

 mentioned, pass along the Haversian canals in the compact substance. 

 These are both arterial and venous, but, according to Todd and Bowman, 

 the two kinds of vessels occupy distinct passages ; and the veins, which are 

 the larger, present, at irregular intervals, pouch-like dilatations calculated to 

 serve as reservoirs for the blood, and to delay its escape from the tissue. 

 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 improperly, 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 



