12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J2. 



observed in the bone of the fish, plate i, figure 2. Around the medul- 

 lary canal are the internal circumferential lamellae forming an enclos- 

 ing ring of irregular widths. Within this ring are also found 

 vascular canals of early Haversian differentiation extending longi- 

 tudinally. Between the external and internal lamellae above 

 described, is a ring of Haversian systems of late differentiation, 

 deficient in the anterior wall and increasing in width in the outer 

 lateral wall as it reaches the posterior ridge. The lacunae are long 

 and narrow with straight canaliculi. 



TANGENTIAL SECTION OF THE SAME FEMUR SHOWING THE 

 CIRCULATION 



Pl. 3, Fig. 30 



Entering canals with and without enclosing lamellae are of fre- 

 quent occurrence. The circulation is a combination of the branching 

 and plexiform types. The central portion is branching and the 

 lateral, plexiform, vascular expansions are not as prominent as they 

 are in many other sections. The section shows the circulatory com- 

 bination of type conforming to the structural type combination. 



CROSS AND TANGENTIAL SECTIONS OF THE FEMUR OF ADULT 

 MAN, A WHITE MALE 



CROSS SECTION SHOWING THE STRUCTURE 



Pl. 4. Fig. 31 



The bone is third type in differentiation with the exception of a 

 portion of the anterior wall where the remains of first type bone are 

 found. The section is composed of completely differentiated Haver- 

 sian systems, some of which are senile. The external circumferential 

 lamellae are fragmentary, while the internal are complete. 



TANGENTIAL SECTION OF THE SAME FEML% SHOWING THE 

 CIRCULATION 



Pl. 4, Fig. 32 



The type of circulation is plexiform with wide, irregularly shaped 

 meshes. Entering vascular canals surrounded by lamellae are seen 

 here and there in the section. Vascular expansions are prominent. 

 This section is taken from the bone represented in plate 4, figure 31, 

 near the periosteal surface of the left side of the drawing and near 

 the posterior ridge. It is difficult to think of the circulation as shown 

 in plate 4, figure 32, as belonging to that locality. 



