14 ANATOMY AND PHYSIOLOGY 



A similar membrane called endosteum lines the canal in the shaft 

 of long bones. It bears the " nutrient" artery which, in the cavity 

 of the shaft, divides into two branches running in the endosteum 

 toward the two extremities. 



The deep layers of the periosteum contain bone-forming cells. 

 (See OSSIFICATION.) 



CLASSIFICATION OF BONES ACCORDING TO SHAPE 



According to differences of shape and arrangement of their 

 tissue, bones are classified as long, short, fiat, and irregular. A 

 long bone has always a shajf of compact tissue, 

 and two enlarged extremities of cancellous tissue 

 with a thin compact covering. The shaft is hol- 

 low, containing yellow marrow, this cavity being 

 called the medullary canal. 



A short bone has neither shaft nor extremity; 

 it is composed of cancellous tissue with a thin 

 compact covering. 



A flat bone is arranged in layers, two of compact 

 tissue with one of spongy or cancellous tissue be- 

 tween them. 



An irregular bone conforms to no special defi- 

 nition. 



REMARKS. In no part of anatomy is it more impor- 

 tant that the student should learn the structures from 

 the actual specimens than in the division called osteology. 

 The bones are to be studied, not the book. It is supposed 

 that with the bone in the hand the student will use the 

 FIG. 9. RIGHT book as a key, by means of which she will become ac- 

 FEMUR ANTERIOR, quainted with the names of its parts and their uses. 

 mE^ol E p T iPHY- The habit of studying the human body itself rather than 

 SES, AND SHAFT OR the description of it cannot be too soon nor too firmly 



P' AP = YSIS - ~~ established. 

 (Morns.) 



OSSIFICATION 



Ossification is the formation of bone from cartilage or mem- 

 brane by the deposit of mineral substances, mostly salts of lime. 

 Flat bones develop in membrane; others in cartilage. 



