VEETEBEAL COLUMN. 87 



direction, ceases. In cases where the epiphysis enters into the formation of a joint, 

 the cartilage over the articular area persists and undergoes neither calcification nor 

 ossification. 



Vascular, Lymph, and Nervous Supply of Bone. From what has been 

 said it will be gathered that the vascular supply of the bone is derived from the 

 vessels of the periosteum. These consist of fine arteries which enter the surface of 

 the diaphysis and epiphysis ; but in addition there is a larger trunk which enters the 

 diaphysis and reaches the medullary cavity. This is called the nutrient artery of 

 the bone. The direction taken by this vessel varies in different bones. In the 

 upper limb the artery runs dis tally in the case of the burner us and proximally 

 in the radius and ulna; in the lower limb the nutrient vessel of the femur is 

 directed towards the proximal extremity of the shaft, whilst in the tibia and fibula 

 it follows a distal course. The direction of the nutrient artery in the bone is 

 a mechanical result of the unequal growth of the two extremities of the bone. 

 During the greater part of intra-uterine life the principal nutrient arteries of the 

 ng bones are directed towards the distal extremity of the limb. In the process 

 development the point of entrance of the artery is turned away from the 

 iphysis which furnishes the greatest amount of bone, and thus, together with 

 e nutrient canal, acquires an obliquity directed towards the extremity of the 

 ne which develops last (Piollet, J. de I'Anat. et de la Phys., 1905, p. 57). 

 It may assist the memory to point out that when all the joints are flexed, as 

 the position occupied by the foetus in utero, the direction taken by the vessels 

 the same, and corresponds to a line passing from the head towards the tail-end 

 if the embryo. Consequently, in the upper limb the vessels run towards the 

 elbow, whilst in the lower limb they pass from the knee. 



The veins which permeate the spongy texture of the bone are large and thin- 

 walled. They do not accompany the arteries, and, as a rule, in long bones they 

 escape through large openings near the articular surfaces. In flat bones they occupy 

 hannels within the diploe, and drain into an adjacent sinus, or form communica- 

 ns with the superficial veins of the scalp. 



The lymph vessels are mainly periosteal, but enter the bone along with the 

 ood-vessels and become perivascular. 



The nerves which accompany the arteries are probably destined for the supply of 

 e coats of these vessels. Whether they end in the bony tissue or not is unknown. 

 The attention of anatomists has long been directed to the elucidation of the laws 

 hich regulate bone-growth. Our present knowledge of the subject may be briefly 

 mmarised in the following generalisations : 



1. In bones with a shaft and two epiphyses, the epiphysis towards which the 

 trient artery is directed is the first to unite with the shaft. 



2. In bones with a shaft and two epiphyses, as a rule the epiphysis which com- 

 nces to ossify latest unites soonest with the shaft. (The fibula is a notable 



exception to this rule.) 



3. In bones with a shaft and one epiphysis the nutrient artery is directed 

 towards the end of the bone which has no epiphysis. (This arrangement holds 

 good in the case of the clavicle, the metacarpus, metatarsus, and phalanges.) 



4. When an epiphysis is ossified from more than one centre, coalescence takes 

 place between the separate ossific nuclei before the epiphysis unites with the shaft. 



Highly suggestive, too, are the following propositions That ossification first 

 commences in the epiphysis which ultimately acquires the largest relative propor- 

 tion to the rest of the bone, and that the ossification of the epiphysis is also 

 correlated with its functional importance. In cases of long bones with only one 

 epiphysis, the epiphysis is placed at the end of the bone where there is most 

 movement. 



COLUIYINA VERTEBRALIS. 



The vertebral column of man consists of thirty-three superposed segments 

 or vertebrae. In the adult, certain of these vertebrae have become fused together 

 in the process of growth to form bones, the segmental arrangement of which 



