10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



TANGENTIAL SECTION OF THE FEMUR OF AN ELK, ALCES 



AMERICANUS, SHOWING THE CIRCULATION 



Pl. 3, Fig. 22 



The type of bone is second. Several perforations in the bone sub- 

 stance for the passage of blood vessels are present. Some of them 

 are surrounded by enclosing lamellae and some are not (Volkmann's 

 canals). The circulation is an extensive plexus of blood vessels with 

 round and irregularly shaped meshes. It has a general direction 

 lengthwise of the bone. 



TANGENTIAL SECTION OF THE FEMUR OF A BELGIAN HARE, 

 LEPUS, SHOWING THE CIRCULATION 



Pl. 3, Fig. 23 



The type of bone is an early second and third. Entering vascular 

 canals through which blood vessels are seen to pass and ramify in 

 the bone substance are present in the central portion of the section. 

 The canals are not surrounded by lamellae. The circulation is a com- 

 bination of a branching and plexiform distribution. The vascular 

 expansions are prominent. One is seen in a vessel shortly after 

 entering the bone. It is a matter of observation in bone circulations 

 that the type of circulation varies with the type of structure. 



TANGENTIAL SECTION OF THE FEMUR OF A BULLDOG, 

 SHOWING THE CIRCULATION 



Pl. 3, Fig. 24 

 The type of bone is second and third. Entering vascular canals, 

 without enclosing lamellae, are seen in the bone substance through 

 which blood vessels are passing. The circulation is a dense branching 

 and plexiform combination. The vessels are small in diameter, fre- 

 quently branching, the union of their branches producing a plexiform 

 efifect. 



CROSS AND TANGENTIAL SECTIONS OF THE FEMUR OF A 

 MONKEY, MACACA RHESUS 



CROSS SECTION SHOWING THE STRUCTURE 



Pl. 3, Fig. 25 



The type of bone is first and third. The section is composed of 

 lamellae interrupted by Haversian systems of early and late diiTer- 

 entiations. Crescents of late Haversian differentiation are found 

 bordering upon the medullary canal in the anterior inner and pos- 

 terior outer wall. The lacunae of the bone are long with straight 

 canaliculi. The principal structure is lamellar and the type is much 

 more first than third. 



