130 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



of lamiiia\ The femur of the mule differs from tlie horse in its predominating 

 proportion of lamina^ and in the frequent senile changes present in its scattering 

 Haversian systems. The difference between the horse and the mule is found in 

 the jackass. 



Type II-III, C. 



LEFT FEMUK OF ELEPHAS INDICUS. ASIATIC ELEPHANT. AMER. MUS. NAT. HIST. 



Pl. n. Fig. 200. Syn. Tab. VII 



Antero-posterior diameter of bone, 121 mm.; lateral, 77 mm. 



Antero-po.sterior diameter of medullary canal, nO mm.; lateral, .'^S mm. 



The medullary canal is full. Medullary index, 25%. 



Struchire. — The section is composed of lamella", laminse, and Haversian 

 systems, the laminae predominating. The posterior ridge is composed of Ha- 

 versian systems with inter-Haversian lamellae. Beginning in the inner side of 

 the ridge and extending around the external sui'face of the posterior inner wall 

 is a wide band of lamellse, frequently interrupted by Haversian systems. The 

 lamella? soon separate into lamina? as they extend around the section. The 

 lamina', frequently interrupted by Haversian systems and crossed by canals, 

 complete the circumference of the bone to the posterior ridge. In the anterior 

 wall they constitute two-thirds, in the inner wall one-third, and in the outer 

 and posterior wall over lialf the width of the wall. As they approach the ridge 

 they shorten and widen into elongated Haversian systems. Thus a wide horse- 

 shoe of lamellse and lamina surrounds the bone. In the anterior wall the toe 

 of this shoe is very narrow, having been displaced by Haversian systems. The 

 lacunae and canaliculi are well developed. Underneath the laminar shoe is an 

 irregularly shaped central ring of well developed Haversian systems witli some 

 senile changes around the medullary canal. The lacuna? are well developed.- 

 Around the medullary canal is an enclosing ring of lamella in the form of 

 cancellous bone. 



The bone is over half laminae and lamella, and exhibits a different type of 

 structure from that seen in the African elephant. 



Type Il-III, C, senile. 



RIGHT KEMli: iiV HIPPOPOl'AMrS AMPniBX'S. HIPPOPOTAM T'S 



I'l,. K. Fi(i. 2(>1. Sy\. Tap.. VII 



Autero-posterior diameter of bone, 7U mm.; lateral, 7U mm. 

 Antero-posterior iliameter of medullary canal, 26 mm.; lateral, 30 mm. 

 The medullary canal is full. ^lediillary index, 19%. 



Structure. — Beginning on the outer side of the posterit)r ridge and extend 

 ing around the hone to the inner wall is a wide l>and of ]amina\ interrupted by 



