90 



STUDIES IN ADVANCED PHYSIOLOGY. 



say from the shaft of the humcrus, be taken, it is found to 

 be not homogeneous at all, but pierced by a set of canals 

 running mainly in a longitudinal direction, known as Haver- 

 sian canals. Through these canals run blood-vessels, nerves 



Fig. 41. TRANSVERSE SECTION FROM THE SHAFT OF THE HUMERUS, SHOWING THRKE 



HAVERSIAN SYSTEMS COMPLETE. 



The Haversian canals, lacunae and canaliculi appear black, being filled with air and 

 debris from the grinding. 



and lymphatics. Around each Haversian canal lie from 

 several to many series of cylindrical plates, or lamellae, 

 between which occur in characteristic rows little openings 

 called lacunae. Running out from each lacuna are many 

 divergent and branching canals called canaliculi, which 

 connect with similar canals from the immediately surround- 

 ing lacunae. The canaliculi of the lacunae next to the 

 Haversian canal open into the Haversian canal. By this 

 system of lacunae and canaliculi nourishment may soak 

 from the Haversian canal through every portion of the bone. 

 These lacunae are in life each filled by a little corpuscle 

 not unlike an ordinary white blood-corpuscle, called an 

 osteoblast. Arms from these osteoblasts extend through the 



