NO. lO THE CIRCULATORY SYSTEM IN BONE: FOOTE II 



TANGENTIAL SECTION OF THE SAME FEMUR, SHOWING THE 

 CIRCULATION 



Pl. 3, Fig. 26 



A few entering vascular canals without surrounding lamellae are 

 present. The circulation is a dense branching type which, here and 

 there, presents a slight appearance of the plexiform distribution. The 

 blood vessels are large and trunk-like in places and a very few vas- 

 cular expansions are present. 



CROSS AND TANGENTIAL SECTIONS OF THE FEMUR OF A 

 9 MONTHS' HUMAN WHITE FETUS 



CROSS SECTION SHOWING THE STRUCTURE 



Pl. 3, Fig. 27 



The section is composed of short laminae with central canals widen- 

 ing and shortening until they are transformed into Haversian sys- 

 tems. External circumferential lamellae surround the section (pos- 

 terior wall excepted) and directly underneath the lamellae is a row 

 of advanced differentiations of Haversian systems. The medullary 

 canal is small, irregular in shape and situated in the anterior half 

 of the section. The posterior wall is composed of Haversian systems 

 of advanced differentiations and in the mid line where the walls of 

 the bone unite is a narrow radiating layer of bone substance which 

 disappears as complete union takes place. 



TANGENTIAL SECTION OF THE SAME FEMUR SHOWING THE 

 CIRCULATION 



Pl. 3, Fig. 28 

 The circulation is plexiform in type, the general direction of which 

 is longitudinal and slightly oblique. The vessels forming the plexus 

 have short branches which seem to disappear in the bone substance 

 within the meshes. Vascular expansions are present, one being 

 shown in the left central portion of the figure. 



CROSS AND TANGENTIAL SECTIONS OF THE FEMUR OF A 

 WHITE CHILD 9 YEARS OLD 



CROSS SECTION SHOWING THE STRUCTURE 



Pl. 3, Fig. 29 



The type of bone is first and third. Around the periphery of the 



section is a wide crescent shaped band of lamellae enclosing numerous 



vascular canals of the earliest Haversian differentiation, such as were 



