BY DR. BURDON-S ANDERSON. 307 



still rises outwards in inspiration; but if these muscles are 

 completely severed, no more costal movement is perceptible ; 

 nor is there any hardening of the exposed intercostal muscles 

 at the moment of inspiration. In a word, it must still be ad- 

 mitted that the action of these muscles is as yet undetermined. 

 Most probably they may be regarded as constrictors of the 

 chest as the agents of forced expiration. 



93. Movements of the Nares and Larynx. In the 

 rabbit, the nostrils dilate with each ordinary inspiration, and 

 contract in expiration; but from their frequency these move- 

 ments are very difficult to observe. To study them satisfac- 

 torily, the student must avail himself of the excessiva*and in- 

 frequent respirations of animals in which both vagi have been 

 divided. It is then seen that the dilatation of the nares is 

 the first act of inspiration. It precedes by a distinct interval 

 the expansion of the chest, and appears even to precede the 

 contraction of the diaphragm. Whether it actually does so 

 is very difficult to determine. The muscles by which this 

 movement is effected are, the subcutaneous faciei which springs 

 from the lateral surface of the intermaxillary bone, and from 

 the anterior supraorbital process of the frontal bone, to be in- 

 serted into the skin of the nose and forehead, and the levator 

 nasi, which springs from the lower edge of the orbit, and is 

 also inserted by a long tendon into the skin, covering the 

 edge of the nose, Of the two, the former is the more super- 

 ficial. 



The respiratory movements of the larynx in the rabbit are 

 scarcely perceptible in perfectly natural breathing; but the 

 slightest interference with the access of air to the chest is suf- 

 ficient to produce them. The larynx is drawn downwards in 

 inspiration by the muscles connecting it with the sternum, 

 and returns to the position of muscular equilibrium in expira- 

 tion. One of these muscles, the sterno-thyroid, has also the 

 effect of tilting forwards the thyroid cartilage, so as to bring 

 its lower edge nearer the cricoid. 



94. To stiuty the intrinsic respirato^ movements of the 

 larynx, the rima glottidis must be exposed to observation, by 

 making a suitable opening either above or below. The best 

 view of the movements is obtained by dividing the hyothyroid 

 membrane. The skin having been carefully divided in the 

 middle line, lege artis, the membrane must be exposed with 

 the aid of two pairs of forceps. The veins (which are the 

 principal source of difficulty) can then be readily seen, and 

 must be carefully secured above and below by ligatures, be- 

 tween which the membrane may be cut across without risk of 

 hemorrhage. The head must of course be so supported that 

 a strong light is thrown on the vocal cords. If now the epi- 

 glottis is drawn forwards, the motions of the vocal cords and 



