36 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



The internal circumferential lamellae surround the medullary canal. They 

 are clearer than those of the external lamellae, their lacunae are oval, their 

 canaliculi are short and partly in the central ring, and there is a large vascular 

 canal on its way to the medullary canal. The internal lamellae are poorly 

 developed. The section shows a threefold division. 



Type I. 



RIGHT FEMUR OF RANA CATESBIANA (MEDIUM SIZED). SECOND BULL FROG. 



CR, MED. COLL. 



Pl. 1, Fig. 2. Syn. Tab. I 



Antero-posterior diameter of bone, 2.5 mm. ; lateral, 3 mm. 

 Antero-posterior diameter of medullary canal, 1.4 mm. ; lateral, 1.6 mm. 

 The medullary canal is full. Medullary index, 42%. 



Structure. — Around the bone is a very narrow ring of dense lamella con- 

 taining a few, long, narrow lacuna? and long canaliculi. 



In the center of the anterior wall is a notch, which is part of the nutrient 

 canal. Beginning a little to the outer side of the posterior mid-line and extend- 

 ing around the outer wall, anterior, and about one-fourth of the inner wall, the 

 entire thickness of the bone is composed of concentric lamellae with oval lacunae 

 and bushy canaliculi. The remaining portion of the bone is composed of con- 

 centric lamellae, which are crossed by short canals, arranged radially in twos 

 and threes. The canals are surrounded by clear areas of bone substance, and 

 extending from them in all directions are very fine canaliculi. The internal 

 circumferential lamellae are not distinct from the remaining structure. Its 

 peculiar feature is the gradual disappearance of the radiating canals. 



Type I. 



right femur of rana catesbiana (small). third bull frog. cr. med. coll. 



Pl. 1. Fig. 3. Syn. Tab. 1 



Antero-posterior diameter of the bone, 1 mm. ; lateral, 1.3 mm. 

 Antero-posterior diameter of the medullary canal, 0.5 mm. ; lateral, 0.6 mm. 

 The medullary canal is full. Medullary index, 29%. 



Structure. — The section is composed of lamella 1 , concentrically arranged 

 around the medullary canal. There are no radiating canals. The lamella 1 are 

 clear, their lacunae oval, long and narrow, and their canaliculi are long and 

 numerous. The section has a uniform structure. 



The peculiar feature is the complete disappearance of the radiating canals. 



These figures show drawings of femora taken from the same species of 

 frogs, but of different sizes and weights. The largest (fig. 1) is lowest in 

 development; the second in size (fig. 2) is next, and the third (fig. 3) is last 



