102 SMITHSONLVN CONTKIBUTIOXS TO KNOWLEDGE VOL. 35 



RIGHT FBMUK OF HYDKOCHCERUS CAfYBAKA. NO. 35325, AMER. MUS. NAT. HIST. 



Pl. 10, Fig. 198. Syn. Tab. V 



Autero-posterior diameter of bone, 22 mm. ; lateral, 20 mm. 



Autero-posterior diameter of medullary canal, 13 mm. ; lateral, 11 mm. 



The medullary canal is full. Medullary index, 48%. 



Structure. — The section is surrounded by a narrow ring of Haversian sys- 

 tems and inter-Haversian lamelte. The central ring, confined to the outer wall, 

 is composed of crude Haversian systems of the (lb) dilferentiatiou, between 

 which are lamellre with large, oval lacuiiEE and bushy canaliculi in the outer wall, 

 and lamellae with oval lacunse and bushy canaliculi interrupted by canals of the 

 (la) differentiation in tlie inner and anterior wall. The internal circumferential 

 lamellge form a narrow ring round t1ie medullary canal. The lacunae are oval. 



Type I-III, la, lb. 



Femora or Fetal Sheep, Calf, and Pig — Half Time 



BIGHT FEMUR OF FETAL SHEEP, 11 WEEKS. NO. 93, CK. MED. COLL. 



Pl. 11, Fig. 199. Syn. Tab. V 



Antero-posterior diameter of bone, 3.5 mm,; lateral, 4 mm. 



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



The medullary canal is full. jMeduUary index, 8%. 



Structure. — The section is comjaosed of short, wide, irregular lamiufe with 

 oval lacunae and bushy canaliculi, between which are short, wide, irreg-ular com- 

 municating canals. The section is pretty uniform in structure. A few Ha- 

 versian systems of the (lb) differentiation are present in the posterior wall. 

 This feuuir is about one-half of tlie full fetal term and may be compared with 

 the human femur of 4 to 5 months. 



Type II-III, lb. 



RIGHT FEMUR OF FETAL CALF, 18 WEEKS. NO. 94, CR. MED. COLL. 



Pl. 11, Fig. 200. Syn. Tab. V 



Antero-posterior diameter of bone, 12 mm.; lateral, 11 mm. 



Antero-posterior diameter of medullary canal, 5 mm.; lateral, 4 mm. 



The medullary canal is full. Medullary index, 18%. 



Structure. — The bone is half fetal development. It is com^josed of small, 

 very irregular areas of laminae separated by many canals of bizarre shapes. 

 Around the circumferential fomtli of the l)one the canals are elongated and 

 the laininte have assumed a general concentric arrangement. In the medul- 

 lary throo-fourths there is no dpfinito plan of arrangement. The laminae are 



