102 



SMITHSONIAN" CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



EIGHT FEMUR OF HYDROCHGERUS CAFYBARA. NO. 35325, AMER. MUS. NAT. HIST. 



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



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

 Antero-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 lamellae. The central ring, confined to the outer wall, 

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

 which are lamellae with large, oval lacunae and bushy canalieuli in the outer wall, 

 and lamelhe with oval lacunae and bushy canalieuli interrupted by canals of the 

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

 lamellae form a narrow ring round the medullary canal. The lacunae are oval. 



Type I-III, la, lb. 



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



right femur of fetal sheep, 11 weeks. no. 93, cr. 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. Medullary index, 8%. 



Structure. — The section is composed of short, wide, irregular laminae with 

 oval lacunae and bushy canalieuli, between which are short, wide, irregular 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 femur is about one-half of the full fetal term and may be compared with 

 the human femur of 4 to 5 months. 



Type II-HI, 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 composed of small, 

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

 Around the circumferential fourth of the bone the canals are elongated and 

 the lamina; have assumed a general concentric arrangement. In the medul- 

 lary three-fourths there is no definite plan of arrangement. The laminae are 



