AUXILIARY MUSCLES OF INSPIRATION. 379 



obliquely downwards and outwards, to be attached to the 

 upper borders of the second, third, fourth, and fifth ribs just 

 beyond their angles. By reversing its action, as we have re- 

 versed the description of its origin and insertions, it is capable 

 of increasing the capacity of the thorax. Sibson has seen 

 this muscle contract in inspiration, in the dog and the ass. 1 



Sterno-mastoideus. That portion of the muscle which is 

 attached to the rnastoid process of the temporal bone and the 

 sternum, when the head is fixed, is capable of acting as a 

 muscle of inspiration. It does not act in ordinary respira- 

 tion, but its contractions can be readily observed whenever 

 respiration is hurried or exaggerated. 



The following muscles, as a rule, only act as muscles of 

 inspiration when respiration is exceedingly difficult or la- 

 bored. In certain cases of capillary bronchitis, for example, 

 the anxious expression of the countenance betrays the sense 

 of impending suffocation ; the head is thrown back and fixed, 

 the shoulders are braced, and every available muscle is 

 brought into action to raise the walls of the thorax. 3 



Levator Anguli /Scapulae and /Superior Portion, of ike 

 Trapezius. Movements of the scapula have often been ob- 

 served in very labored respiration. Its elevation during in- 

 spiration is chiefly effected by the levator anguli scapulae 

 and the upper portion of the trapezius. The former arises 

 from the transverse processes of the upper three or four cer- 

 vical vertebrae, and is inserted into the posterior border of 

 the scapula below the angle. It is a thick flat muscle, and 

 when the neck is the fixed point, assists in the elevation of 

 the thorax by raising the scapula. The trapezius is a broad 

 flat muscle arising from the occipital protuberance, part of 

 the superior curved line of the occipital bone, the ligamentum 



1 Op. tit., p. 521. 



2 Under these circumstances, some muscles which we have not thought it ne- 

 cessary to enumerate may act indirectly as muscles of inspiration. 



