NO. 10 THE CIRCULATORY SYSTEM IN BONEi FOOTE 7 



RECONSTRUCTION OF A SECOND TYPE BONE WITH ITS INTER- 

 LAMINAR CIRCULATION 



Pl. 2, Fig. io 



This figure shows a reconstruction of a second type bone with its 

 circulation. The drawing represents three concentric laminae with 

 two interlaminar plexuses of blood vessels. The vessels are uniform 

 in size, composed of thin connective tissue walls and the vascular 

 expansions are not at all prominent. It is difficult to understand why 

 such a rich blood supply should be required in bone for its nutrition. 



CROSS AND TANGENTIAL SECTIONS OF AN EARLY DIFFERENTI- 

 ATION OF A THIRD TYPE BONE IN BIRDS AS SEEN IN THE 

 FEMUR OF A TURKEY BUZZARD, CATHARTES 

 AURA SEPTENTRIONALIS 



CROSS SECTION SHOWING THE STRUCTURE 



Pl. 2, Fig. ii 



This bone is more advanced in differentiation than that of the 

 domestic turkey since it is composed of third type structural bone 

 units instead of the second. These units are enclosed between the 

 external and internal circumferential lamellae and form nearly the 

 whole bone structure. 



TANGENTIAL SECTION OF THE FEMUR OF THE SAME ANIMAL SHOWING 



THE CIRCULATION 



Pl. 2, Fig. i2 



The meshes of the circulatory plexus are longer and enclose larger 

 bone areas than those seen in the femur of the turkey. The vascular 

 expansions are not as prominent as they are in some of the other 

 bones, but may be seen here and there. A general plexiform plan of 

 circulation is evident, but an elongation of the meshes in the central 

 portion shows a slight variation in the circulatory distribution. 



TANGENTIAL SECTION OF THE FEMUR OF A DOMESTIC 

 CHICKEN, CALLUS 



Pl. 2, Fig. 13 



The type of structure is a first and early third. Several entering 

 canals without surrounding lamellae are present. The circulation 

 appears as a rich plexus of small blood vessels coming off from a 

 central vessel which extends lengthwise of the section. The meshes 

 of the plexus are small, round, oval or irregular in shape and the 

 lacunae of the bone substance are round or oval with short, branching 

 canaliculi. 



