NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 103 



composed of oval and long lacunse with rather infrequent oanalionli. Here and 

 tliere, and especially in the posterior ridge, some laminie^ have widened, short- 

 ened, and assumed in part the shape of Haversian systems. 

 Type II-III, lb. 



RIGHT FEMVR OF A FETAL, PIG, HALF FETAL PERIOD 8^ WEEKS. 



Pl. n, Fig. 201. Syn. Tais. V 



Antero-posterior diameter of bone, 3.5 mm. ; lateral, 3 mm. 



Antero-posterior diameter of medullary canal, 1.5 nnn. ; lateral, 1 mm. 



The medullary canal is situated eccentrically. The anterior wall is tliin- 

 nest, the posterior thickest. 



The medullary canal is full. Medullary index, 17%. 



Structure. — The section is composed of concentric laminfe separated and 

 crossed by wide canals. In tlie anterior wall the laminae are short, in the lateral 

 wall, long, and in the posterior wall, irregular. There are no Haversian sys- 

 tems, although in the posterior wall the laminae are very short and inclined to a 

 circular bend. The lacunae are oval and the canaliculi are bushy. 



Type II. 



FEMLTIi OF CARIACUS MACROTIS. DEER. OR. MED. COLL. 



Pl. 11, Fig. 303. Syn. Tab. V 



Antero-posterior diameter of bone, 25 mm. ; lateral, 24 mm. 



Antero-posterior diameter of the medullary canal, 17 nnn. ; lateral, 16.5 mm. 



The medullary canal is full. Medullary index, 88%. 



Strvctiire. — Tlie bone is composed almost entirely of lamiiia\ Tliey are 

 well developed, separated, and crossed by wide canals. Tlieir lacunae are long, 

 narrow, and completely developed and the canaliculi are long and branching. 

 Here and there are found a few aberrant Haversian systems, produced by a 

 circular widening of the concentric canals and the bending of a few lamellae 

 around the circular openings. The laminae form the entire section, excepting 

 the posterior ridge and a small area near the anterior wall which are composed 

 of Haversian systems with many oval lacuiife. There are no distinct external 

 circumferential lamellae. The canals between the laminae cross them at right 

 angles and communicate freely with each other. 



The internal circumferential lamina^ form an irregularly sliaped boundary 

 of the medullary canal. They are frequently crossed by canals extending out- 

 ward from the medullary canal. The surface of the posterior ridge shows the 

 tendon attachments of muscles. Extending from this surface to the internal 

 circumferential lamina^, and for a short distance on either side of the posterior 

 mid-line, is an area of Haversian systems. They are irregular in shape, well 



