428 MOVEMENTS 



the production of sarcolactic acid, and consequently the reaction of the 

 muscles becomes acid. During contraction a muscle consumes oxygen 

 and gives off carbon dioxide. It is probable, also, that other katabolic 

 products are formed in the same way. 



Rigor Mortis. At a certain time after death, the entire voluntary 

 muscular system becomes rigid, and the muscles will not contract under 

 stimulation. This is due to a gradual coagulation of the muscle-plasma. 

 During this process the muscles contract and give off heat and carbon 

 dioxide in small quantities. The muscles first affected usually are those 

 of the neck and lower jaw and the rigidity gradually extends to the feet. 

 Cadaveric rigidity begins in fifteen minutes to seven or eight hours after 

 death and lasts until putrefaction sets in. It disappears in the same 

 order, as regards different muscles, in which it began and extended. 



PASSIVE ORGANS OF LOCOMOTION 



The study of locomotion involves a knowledge of the physiological 

 anatomy of certain passive organs, such as the bones, cartilages and liga- 

 ments. Although a complete history of the structure of these parts 

 trenches somewhat on the domain of anatomy, a brief description of 

 their histology will practically complete the account of the tissues of the 

 body, with the exception of the nervous system and the organs of re- 

 production, which will be taken up hereafter. 



Locomotion is effected by the action of muscles on certain passive 

 movable parts. These are the bones, cartilages, ligaments, aponeuroses 

 and tendons. The fibrous structures have already been described, and 

 it remains only to study the structure of bones and cartilages. 



Physiological Anatomy of the Bones. The bones are composed of 

 what is called the fundamental substance, with cavities and canals of 

 peculiar form. The cavities contain corpuscular bodies called bone- 

 corpuscles. The canals of larger size serve for the passage of blood- 

 vessels, while the smaller canals (canaliculi) connect the cavities with 

 each other and finally with the vascular tube (see Plate X, Fig. 2). 

 Many of the bones present a medullary cavity filled with a peculiar 

 structure called marrow. In almost all bones there are two distinct por- 

 tions ; one, that is exceedingly compact, and the other, more or less 

 spongy, or cancellated. The bones are invested with a membrane, 

 containing vessels and nerves, called periosteum. 



The fundamental substance is composed of an organic matter, called 

 ossein, combined with various inorganic salts, in which calcium phos- 

 phate largely predominates. In addition to calcium phosphate, the 

 bones contain calcium carbonate, calcium fluoride, magnesium phos- 



