56 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



vol. 35 



LEFT FEMUR OF THE SAME PYTHON BEGIUS. U. S. NAT. MUS. 



Pl. 4, Fig. 64. Syn. Tab. II 



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

 Antero-posterior diameter of medullary canal, 0.5 mm. ; lateral, 0.4 mm. 

 The medullary canal is full. Medullary index, 28%. 



Structure.- — The section is composed of two rings of lamellae, viz. : external 

 and internal. The external is thickest and is composed of lamellae with a few 

 round and oval lacunae and bushy canaliculi. The canaliculi of the posterior 

 wall are long and straight and, in the anterior wall, infrequent and bushy. A 

 narrow ring of internal lamella! with long lacunae and straight canaliculi sur- 

 rounds the medullary canal. 



Type I. 



LEFT FEMUR OF ALLIGATOR MISSISSIPPIENSIS. ALLIGATOR. CR. MED. COLL. 



Pl. 4, Fig. 65. Syn. Tab. II 



Antero-posterior diameter of bone, 17 mm.; lateral, 15 mm. 

 Antero-posterior diameter of medullary canal, 7 mm. ; lateral, 6 mm. 

 The medullary canal is full. Medullary index, 20%. 



Structure. — A thin cross-section of this femur held up to the light presents 

 a ringed appearance like that of a cross-section of the trunk of a tree. 



The section is composed of three concentric rings of laminae with long, nar- 

 row lacunas and straight canaliculi, alternating with four concentric rings of 

 bone substance enclosing crude Haversian canals. The Haversian canals are 

 round, oval, or irregular in shape, are large and small in size, and very numer- 

 ous. They are surrounded by clear areas of bone substance and many fine cana- 

 liculi from concentric adjacent oval lacunae pass radially across the areas of bone 

 substance into the canals. The (lb) stage of the Haversian system is repre- 

 sented. The laminae are fairly well developed. 



Type I-II-III, la, lb. 



FEMUR OF CHELYDBA SEBPENTINA. SNAPPING TUETLE. CR. MED. COLL. 



Pl. 4, Fig. 66. Syn. Tab. II 



Antero-posterior diameter of bone, 8 mm. ; lateral, 8.5 mm. 

 Antero-posterior diameter of medullary canal, 1 mm. ; lateral, 1 mm. 

 The medullary canal is full. Medullary index, 1.5%. 



Structure. — The wall of the shaft is very thick, proportionately, and the 

 medullary canal is very small. The femur is nearly solid. The section has 

 four concentric rings of laminae alternating with three concentric rings of bone 

 substance in which are many Haversian canals. The canals are much more 

 regular in shape than they were in the alligator and are surrounded by smaller, 



