178 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



the middle of the wall (fig. 363E), and the third is noai' the medullary canal 

 (fig. 363F). From these groups of vessels small branches originate, and from 

 the branches intricate plexuses of minute vessels are formed and occupy the 

 intervals between the groups of large vessels. The posterior w^all is composed, 

 almost entirely, of plexuses of blood vessels and a little bone substance with a 

 few oval lacunae between them. Figure 363a is an enlarged drawing of figure 

 363A. In this bone may be seen an Haversian system formation unlike any 

 noticed in other femora. A short branch is given off from one of the large 

 concentric vessels (figs. 363-1 and 363al) and divides into small branches, which 

 assume a circular arrangement (fig. 363a2). The small branches send off numer- 

 ous twigs which break into capillaries and surround a central opening (fig. 

 363a3). This gives the whole figure a circular form. Slight enlargements of 

 the peripheral capillaries are nipped oft" at intervals, from which arise many 

 minute canals (fig. 363a4). The enlargements become lacunae and the minute 

 canals canaliculi (fig. 363a5). The lacuna? are round and tlie canaliculi are long 

 and straight. 



From this it would appear that the foundations of Haversian systems are 

 laiil in tlie vascular system. Osteoblasts either lodge in the capillaries or are 

 produced by endothelium, and by growth and obstruction to the circulation, 

 separate, throw out processes, and secrete bone substance in which they are 

 enclosed. In this manner an Haversian system seems to be formed. These 

 developments take place in the concentric intervals or rings between the con- 

 centric groups of vessels and transform them into bone (fig. 363B). In this 

 femur the intervals between the three vascular groups are occupied by Ha- 

 versian systems. At quite regular intervals large, irregularly shaped spaces 

 occur, the significance of which does not appear (fig. 363C). Although this bone 

 presents great vascularity, yet it is hard enough to be sawed. Around the 

 external and medullary surfaces the bone formation is farther advance<l. La- 

 melhe are beginning to be evident in these regions. 



Type III, la, lb. 



FEMUR OF AN E(iVPTIAN CHILD. NO. 125(547!) (d ) , U. S. NAT. MUS. 



Fl. 37, Fid. ;!(M. Syn. Tah. IX 



Antero-posterior diameter of bone, W.5 nnn.; lateral, 10 mm. 



Anteroposterior diametei- of medullary canal, 4 mm.; latei'al, 5 mm. 



The medullary canal is full. Medullary index, "IT^/o. 



Structure. — The bone is nearly round. The posterior ridge is coarsely 

 serrat(j<l on its cxtci-iia! sui't'acc. The seiTations consist of jjrojecting Ioojjs of 

 lamellae, enclosing long, elliptical canals and jircsenting the appearance of rather 

 crude Haversian systems. Underneath the serrated border the ridge is com- 

 posed of bone substance enclosing more or less circularly shaped spaces. Some 



