56 



GENERAL ANATOMY. 



(situated in most cases near the centre of the shaft), and perforates obliquely the 

 compact structure. The medullary or nutrient artery, usually accompanied by 

 one or two veins, sends branches upward and downward to supply the medullary 

 membrane, which lines the central cavity and the adjoining canals. The ramifica- 

 tions of this vessel anastomose with the arteries both of the cancellous and com- 

 pact tissues. In most of the flat, and in many of the short spongy bones, one 

 or more large apertures are observed, which transmit, to the central parts of the 

 bone, vessels corresponding to the medullary arteries and veins. The veins emerge 

 from the long bones in three places (Kb'lliker) : (1) by one or two large veins, 

 which accompany the artery ; (2) by numerous large and small veins at the artic- 

 ular extremities ; (3) by many small veins which arise in the compact substance. 

 In the flat cranial bones the veins are large, very numerous, and run in tortuous 

 canals in the diploic tissue, the sides of the canals being formed by a thin lamella 

 of bone, perforated here and there for the passage of branches from the adjacent 

 cancelli. The same condition is also found in all cancellous tissue, the veins being 

 enclosed and supported by osseous structure and having exceedingly thin coats. 

 When the bony structure is divided, the vessels remain patulous, and do not con- 

 tract in the canals in which they are contained. Hence the constant occurrence 

 of purulent absorption after amputation in those cases where the stump becomes 

 inflamed and the cancellous tissue is infiltrated and bathed in pus. 



Lymphatic vessels, in addition to those found in the periosteum, have been 

 traced by Cruikshank, into the substance of bone, and Klein describes them as 

 running in the Haversian canals. 



Nerves are distributed freely to the periosteum, and accompany the nutrient 

 arteries into the interior of the bone. They are said by Kb'lliker to be most 



numerous in the articular extremities 

 of the long bones, in the vertebrae and 

 the larger flat bones. 



Minute Anatomy. The intimate 

 structure of bone, which in all essential 

 particulars is identical in the compact 

 and cancellous tissue, is most easily 

 studied in a transverse section from the 

 compact wall of one of the long bones 

 after maceration, such as is shown in 

 Fig. 26. 



If this is examined with a rather 

 low power the bone will be seen to be 

 mapped out into a number of circular 

 districts, each one of which consists of 

 a central hole, surrounded by a number 

 of concentric rings. These districts are 

 termed Haversian systems ; the central 

 hole is an Haversian canal., and the 

 rings around are layers of bone-tissue 

 arranged concentrically around the cen- 

 tral canal, and termed lamella?. More- 

 over, on closer examination, it will be found that between these lamellae, and 

 therefore also arranged concentrically around the central canal, are a number of 

 little dark specks, the lacuna*, and that these lacunae are connected with each 

 other and with the central Haversian canal by a number of fine dark lines, which 

 radiate like the spokes of a wheel and are called canaliculi. All these structures 

 the concentric lamellae, the lacunae, and the canaliculi may be seen in any 

 single Haversian system, forming a circular district round a central, Haversian, 

 canal. Between these circular systems, filling in the irregular intervals which are 

 left between them, are other lamellae, with their lacunae and canaliculi, running in 



FIG 26. From a transverse section of the shaft of 

 the humerus. Magnified 350 times, a. Haversian 

 canals. 6. Lacunae, with their canaliculi in the lamellae 

 of these canals, c. Lacunae of the interstitial lamellae. 

 d. Others at the surface of the Haversian systems, with 

 canaliculi given off from one side. 



