MINUTE ANATOMY OF BONE. 3 



uli calciferi. They are exceedingly fine tubules, and aid 

 in the distribution of the pabulum of the bone. This 

 arrangement of the Haversian canals, lacunas, and 

 canaliculi is known as the Haversian system, and is most 

 perfectly developed in the long bones. It is, however, 

 also found in the other bones, and even in the fibres and 

 lamella of the spongy tissue, where the thickness of the 

 plates is at all considerable. As the Haversian canals 

 run parallel with the long axis of a bone, therefore a 

 longitudinal section will show the Haversian canals 

 as laid open, and they appear as grooves, at the sides 

 of which the lacunae are arranged in rows or lamellae. 

 Passing between the lacunae, and from them to the 

 Haversian canals, are the canaliculi, as in a transverse 

 section. The Haversian canals frequently divide or 

 branch, rarely running farther than for a distance of two 

 or three lines without bifurcating or receiving a branch 

 of communication. They vary in size from y^TT * ^TTF 

 inch in diameter. Now and then a large canal is 

 seen, but is then partly filled with marrow. These 

 canals serve for the transmission of the blood-vessels 

 and lymphatics, and also for a few nerves, principally 

 branches of the sympathetic. Spinal nerves, when 

 traced into bone, are, as a rule, distributed to the articular 

 extremities. The lacunae are minute cavities hollowed 

 out in the bone-substance. They are ovoidal in form, 

 somewhat flattened or compressed, and average in length 

 T -gVff inch, in width -g-^V^ mcn > and in depth ^V^ inch. 

 They are formed, as are all other spaces in bone, by 

 absorption, and lodge a cell with numerous processes. 



The following diagram represents the relation of the 

 lacunae to each other, and, as is seen, they are simply 

 chambers for the lodgment of multipolar cells, each 

 pole or process lying in a canaliculus and anastomosing 



