324 FACIAL AND LARYNGEAL RESPIRATION. [BOOK n. 



slight, expenditure of muscular energy to bring the chest 

 more rapidly to its former condition. This is, as we have 

 seen, supposed by many to be afforded by the internal inter- 

 costals acting as depressors of the ribs. If these do not act in 

 this way, we may suppose that the elastic return of the abdominal 

 walls is accompanied and assisted by a contraction of the abdominal 

 muscles. The triangularis sterni, the effect of whose contraction is 

 to pull down the costal cartilages, may also be regarded as an ex- 

 piratory muscle. 



When expiration becomes laboured, the abdominal muscles 

 become important expiratory agents. By pressing on the contents 

 of the abdomen, they thrust them and therefore the diaphragm 

 also up towards the chest, the vertical diameter of which is 

 thereby lessened, while by pulling down the sternum and the 

 middle and lower ribs they lessen also the cavity of the chest in its 

 antero-posterior and transverse diameters. They are in fact the 

 chief expiratory muscles, though they are doubtless assisted by 

 the serratus posticus inferior and portions of the sacro-lumbalis, 

 since when the diaphragm is not contracting, the depression of the 

 lower ribs which the contraction of these muscles causes, serves 

 only to narrow the chest. As expiration becomes more and more 

 forced, every muscle in the body which can either by contracting 

 depress the ribs, or press on the abdominal viscera, or afford fixed 

 support to muscles having those actions, is called into play. 



Facial and Laryngeal Respiration. The thoracic respiratory 

 movements are accompanied by associated respiratory movements 

 of other parts of the body, more particularly of the face and of the 

 glottis. 



In normal healthy respiration the current of air which passes 

 in and out of the lungs, travels, not through the mouth but through 

 the nose, chiefly through the lower nasal meatus. The ingoing air, 

 by exposure to the vascular mucous membrane of the narrow and 

 winding nasal passages, is more efficiently warmed than it would be 

 if it passed through the mouth ; and at the same time the mouth 

 is thereby protected from the desiccating effect of the continual 

 inroad of comparatively dry air. 



During each inspiratory effort the nostrils are expanded, pro- 

 bably by the action of the dilatores naris, and thus the entrance of 

 air facilitated. The return to their previous condition during expi- 

 ration is effected by the elasticity of the nasal cartilages, assisted 

 perhaps by the compressores naris. This movement of the nostrils, 

 perceptible in many people, even during tranquil breathing, becomes 

 very obvious in laboured respiration. 



When the mouth is closed, the soft palate which is held some- 

 what tense, is swayed by the respiratory current, but entirely in a 

 passive manner, and it is not until the larynx is reached by the in- 

 going air that any active movements are met with. When the 



