RECORDING RESPIRATORY MOVEMENTS 279 



which may occur to a slight degree in speaking, singing, etc., as well as in 

 the case of many involuntary and reflex acts, such as coughing, sneezing, 

 etc., other muscles are involved. Of these the principal are the abdominal 

 muscles, obliquus externus and internus, rectus abdominis, transversus ab- 

 do minis and pyramidalis. These act, first, by pressing the abdominal 

 viscera against the diaphragm and thereby forcing it up, their descent into 

 the pelvic cavity being prevented; second, by their attachments to the lower 

 ribs and cartilages, the muscles draw these downward and inward, thereby 

 lessening the size of the thoracic cavity; lastly, by their contraction, they 

 form a fixed point for the action of that part of the internal intercostals, 

 not involved in inspiration, to approximate the ribs. 



When by the efforts of the expiratory muscles the chest has been squeezed 

 to less than its average diameters, it again, on relaxation of the muscles, 

 returns to the normal dimensions by virtue of its elasticity. The construc- 

 tion of the chest walls, therefore, admirably adapts them for recoiling against 

 and resisting as well undue contraction as undue dilatation. 



Respiratory Movements of the Nostrils and of the Glottis. During 

 the action of the inspiratory muscles which directly draw air into the chest, 

 those which guard the opening through which the air enters are also active. 

 In hurried breathing the dilatation of the nostrils is well seen, although 

 under ordinary conditions it may not be noticeable. The opening at the 

 upper part of the larynx, however, the rima glottidis, is dilated at each in- 

 spiration for the more ready passage of air, and becomes smaller at each 

 expiration; its condition, therefore, corresponds during respiration with 

 that of the walls of the chest. There is a further likeness between the two 

 acts in that, under ordinary circumstances, the dilatation of the rima glot- 

 tidis is a muscular act and its contraction chiefly an elastic recoil; although, 

 under various special conditions to be hereafter mentioned, there may be 

 considerable muscular contraction exercised. 



Methods of Recording Respiratory Movements. The movements of respira- 

 tion may be recorded graphically in several ways. The ordinary method is to 

 introduce a tube into the trachea of an animal, and to connect this tube by 

 some gutta-percha tubing with a T-piece, the side branch of which is connected 

 with a Marey's tambour, which may be made to write on a recording surface, 

 figure 173. If the tube attached to the free limb of the T-piece be partially 

 closed with a screw compress, the movements of inspiration and expiration are 

 larger than if it were open. The alteration of the pressure within the lungs on 

 inspiration and expiration is shown by the movement of the column of air in 

 the trachea and in its extension to the T-piece. By these means a record of the 

 respiratory movements may be obtained. 



Various instruments have been devised for recording the movements of 

 the chest by application of apparatus to the exterior. Such is the stethometer 

 of Burdon- Sanderson, figure 233. This consists of a frame formed of two 

 parallel steel bars joined by a third at one end. At the free end of the bars 

 is attached a leather strap, by means of which the apparatus may be suspended 



