EXPANSION OF THE THORAX. 807 



some, attributed to the habitual use of stays, but which may be a pro- 

 vision against the occasional impediment to abdominal respiration, 

 which occurs in that sex. Over-distension of the abdomen, from any 

 cause, as from gaseous or solid accumulations in the large intestine, 

 tumors, or dropsical effusions, hinders abdominal respiration, the em- 

 barrassment to which is shown by the special efforts made to perform 

 costal respiration. If the diaphragm contracted by itself, it would 

 not only draw down its own tendinous vault, but would also pull the 

 lower ribs downwards and backwards towards the vertebral column, 

 and so diminish the lateral and antero-posterior dimensions of the 

 lower part of the chest; but, in ordinary, and in deep inspiration, 

 this tendency is counteracted by a proper adjustment of the force 

 which raises the ribs. 



The elevation of the ribs in inspiration is accomplished, in ordinary 

 breathing, by the co-operation of a number of small muscles placed 

 deeply between and upon the ribs. First, more especially concerned, 

 are the external intercostal muscles. These occupy the interspaces 

 between all the ribs, extending, in each intercostal space, from close 

 to the vertebral column to the neighborhood of the costal cartilages ; 

 their fibres pass downwards and forwards, from one rib to another 

 (see Fig. 4). It was at one time supposed that these muscles, being 

 placed between adjacent ribs, could not elevate those bones, unless the 

 uppermost rib was first fixed, but that then each intercostal muscle 

 could raise the rib below it. It has been shown, however, by obser- 

 vations on living animals, that the action of these muscles in elevating 

 the ribs, does not require the previous fixing of the first rib. The 

 mechanical principle on which this apparently singular result depends, 

 maybe illustrated by a simple apparatus, consisting of an upright 

 support of wood, to which two bars are so attached at one end, by 

 means of pins, as to be capable of being elevated or depressed ; the 

 bars themselves being held horizontally, a piece of vulcanized India- 

 rubber is fixed tensely, and obliquely downwards and forwards from 

 the upright support, between the bars i. e., in the same direction as 

 the fibres of the external intercostal muscles. When, now, the bars 

 are drawn down, the India-rubber is stretched, and on being left free 

 to act, immediately elevates both bars again, and supports them even 

 in an oblique direction upwards. The explanation of this result is as 

 follows: the elastic force tends to approximate the ends of the piece 

 of vulcanized India-rubber ; this can only be accomplished by such a 

 motion of the movable bars as will bring the points, to which the ends 

 of the India-rubber are fixed, as near together, i. e., as nearly verti- 

 cal to each other as possible ; and this results in the joint elevation 

 of both bars. In the living body, the vertebral column represents the 

 upright support, and the ribs the bars ; but the effect is here modified 

 by the somewhat fixed condition of the cartilages of the ribs to the 

 sternum, which bone is, accordingly, moved upwards and forwards. 

 Secondly, there are found at the back of the chest, near the spine, and 

 descending from the several dorsal vertebrae to the subjacent ribs, 

 muscles known as the long and short levators of the ribs. These not 

 only assist in elevating the hinder parts of the ribs, but also slightly 



