BONE 



307 



which passes downwards and fprwards from the skull to 

 this pulley, after traversing it, runs upwards and forwards 

 to the lower jaw (Fig. 93). 



9. The General and Minute Structure of Bone. — A 

 fresh long bone such as the femur and humerus of a 

 rabbit, from which the attached muscles, tendons and 

 ligaments have been carefully cleaned away, but the 

 surface of which has not been scraped or otherwise in- 

 jured, is an excellent subject for the study of bone. It is 

 a hard tough body which is flexible and highly elastic 

 within narrow limits, but readily breaks, with a clean 



Fig. 93. — The Codrse of the Digastric Muscle. 



D, its posterior belly ; D', its anterior belly ; between the two is the tendon 

 passing through its pulley connected with Hy, the hyoid bone. 



fracture, if it is pressed too far. The two articular ends 

 are coated by a layer of cartilage which is thickest in the 

 middle. Where the margins of the cartilage thin out a 

 layer of vascular connective tissue commences, and ex- 

 tending over the whole shaft, to the surface of which it is 

 closely adherent, constitutes the periosteum. If the 

 bone is macerated for some time in water, the periosteum 

 may be stripped off in shreds with the forceps. Filaments 

 pass from its inner surface into the interior of the bone. 

 If the shaft is broken across it Avill be found to contain a 



X 2 



