PHYSIOLOGICAL ANATOMY OF THE BONES. 481 



effort, the action is different. In the latter instance, a certain preparation 

 for the muscular effort is made by inflating the lungs, closing the glottis 

 and contracting more or less forcibly the expiratory muscles so as to render 

 the thorax rigid and unyielding ; and by a concentrated effort of the will, the 

 proper muscles are then brought into action. This action of the muscles of 

 the thorax and abdomen, due to simple effort and independent of the partic- 

 ular muscular act that is to be accomplished, compresses the contents of the 

 rectum and bladder and obstructs very materially the venous circulation in the 

 large vessels. It is well known that hernia frequently is produced in this 

 way ; the veins of the face and neck become turgid ; the conjunctiva may be- 

 come ecchymosed ; and sometimes aneurismal sacs are ruptured. An effort 

 of this kind is generally of short duration, and it can not, indeed, be pro- 

 longed beyond the time during which respiration can be conveniently arrested. 

 There are degrees of effort which are not attended with this powerful ac- 

 tion of the muscles of the chest and abdomen, and in which the glottis is 

 not completely closed ; and an opening into the trachea or larynx, rendering 

 immobility of the thorax impossible, does not interfere with certain acts that 

 require considerable muscular power. If the glottis be exposed in a dog, 

 when he makes violent efforts to escape, the opening is firmly closed. This 

 is often observed in vivisections ; but Longet has shown that dogs with an 

 opening into the trachea are frequently able to run and leap with " astonish- 

 ing agility." He also saw a horse, with a large canula in the trachea, that 

 performed severe labor and drew heavily loaded wagons in the streets of Paris. 



PASSIVE ORGANS OF LOCOMOTION. 



It would be out of place to describe fully and in detail all of the varied 

 and complex movements produced by muscular action. Many of these, such 

 as the movements of deglutition and of respiration, are necessarily consid- 

 ered in connection with the functions of which they form a part; but 

 others are purely anatomical questions. Associated and antagonistic move- 

 ments, automatic and reflex movements etc., belong to the history of the 

 motor nerves and will be fully considered in connection with the physiology 

 of the nervous system. 



The study of locomotion involves a knowledge of the physiological anat- 

 omy of certain passive organs, such as the bones, cartilages and ligaments. 

 Although a complete history of the structure of these parts trenches some- 

 what upon the domain of anatomy, a brief description of their histology will 

 practically complete the account of the tissues of the body, with the excep- 

 tion of the nervous system and the organs of generation, which will be 

 taken up hereafter. 



Locomotion is effected by the muscles acting upon certain passive, mov- 

 able parts. These are the bones, cartilages, ligaments, aponeuroses and ten- 

 dons. The fibrous structures have already been described, and it only remains 

 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. 



