NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 143 



Structure.— The section is surroimded by external circumferential lamelte. 

 In the anterior and posterior inner wall the ring is thick and interrupted by 

 Haversian systems of the (la) differentiation. Tlie lacunas are long and narrow 

 and the canaliculi are long. 



Tlie centra] ring is composed of irregularly shaped Haversian systems well 

 developed. It gradually increases in thickness in the inner wall until it reaches 

 about the middle, where it forms two-thirds of the width of the wall. From this 

 point it continues to increase to the middle of the anterior wall, where it forms 

 four-fifths of the bone. Tlie systems are strongly developed, their lacuna are 

 long and narrow, and their canaliculi are long and branching. Between tlie 

 systems are short lamellae. The Haversian canals frequently unite. 



A ring of internal circumferential laminae of varying thickness surrounds 

 the medullary canal. In the inner wall and extending around the posterior 

 region are short, oblique laminae, forming, in some places, nearly one-half of the 

 tliickness of the bone. In the outer wall two or three laminae form the medul- 

 lary boundary. The lacunae are long and narrow and the canaliculi are long 

 and branching. 



Type I-II-III, la, C. 



OS PENIS OF THE RACCOON 



PL. 20, Fig. 288. Stn. Tab. VII 



The OS penis is introduced here because of its relation to the general bone 

 structure of the animal and its relation of structure to function. 



The antero-posterior diameter of the bone is 4 mm. ; lateral, 4 nun. 



The antero-posterior diameter of the central canal is 0.8 mm. ; lateral, 0.8 

 mm. 



The canal is very irregiilar in shape. The bone is of medium hardness. 



The medullary canal is full. Medullary index, 4%. 



Structure. — External circumferential lamelte, rather incompletely devel- 

 oped, surround the bone. They are not equally distinct in all parts. In some 

 places they are fairly well developed, while in others they are indistinct and 

 interrupted by small, incomplete Haversian systems. The lacunae are large, 

 few in number, oval in shape, and have branching canaliculi. 



A wide ring of large and small Haversian systems constitutes the central 

 ring. The large systems occupy the inner portion of the ring, the small ones 

 the outer portion. They are all fairly well developed. Their Haversian canals 

 frequently communicate with each other; their cross-sections are circular; their 

 lacunae are few, long, and narrow; tlieir canaliculi are long and branching; and 

 their lamellje are not clearly defined. Here and there short inter-Haversian 

 lamellae appear. 



