1048 



THORAX. 



ribs is very oblique"; the spine is curved ; 

 therefore the relation of the ribs to the spine is 

 different according to the curve, as are the 

 bars to the body representing the spine 

 (fig. 679.). It will be seen that the inferior six 

 or seven ribs are at a more oblique angle to 

 the spine than the superior ribs. The spine 

 does not curve sufficiently to bring the upper 

 ribs to an angle of 90 with the spine; there- 

 fore, if all the ribs were raised simultane- 

 ously, they would all increase the breadth of 

 their intercostal spaces, whilst their sternal 

 end would recede from the vertebrae, and thus, 

 by their elevation, the thoracic cavity would 

 be enlarged, until they attained the angle of 

 90 to the spine. But if the elevation were 

 carried beyond this point, the intercostal 

 spaces would diminish, and thus the thoracic 

 cavity would decrease. Fig. 684. is a pos- 

 terior view showing the sloping position of 

 the ribs more clearly. Now, if the spine 

 were perfectly erect, the ribs would have a 

 greater range, and consequently the upper 

 ribs could be elevated higher, and thus still 

 more increase the thoracic cavity. A man 



Fig. 680. 



Tlwrax as at death. 



can expire a greater volume of air when 

 perfectly erect, than in any other position. 

 On the other hand, if we curve the spine, 

 we limit the divergence of the ribs, because 

 then we bring the ribs more into the po- 

 sition of a b and a' b' (fig. 678.). Thus, 

 in diseases of the spine, when angular cur- 

 vature is extensive, the ribs are materially 

 limited in their capability of increasing the 

 perpendicular depth of their intercostal spaces, 

 and consequently the perpendicular depth of 

 the thorax. 



Fig. 666. is an instance of angular spine, 

 reducing the ribs to their minimum distances 

 without their moving. We have found by ex- 

 periment, that the greatest volume of air which 

 persons with angular spine can expire, is little 

 more than equal to the volume of air of an 

 ordinary respiration ; i. e. from 20 to 40 cubic 

 inches, instead of 180 to 200 cubic inches. 



The following experiment proves that the 



ribs are all elevated when the chest is inflated, 

 and that the spine is straightened. Into the 

 thorax (fig- 680. et seq.) we insufflated, or 

 forced into the lungs 310 cubic inches of air, 

 and a second cast was taken. The changed 

 position of the ribs and spine is represented in 

 figs. 681. 683. and 685. where it will be seen 

 that all the ribs are raised ; their perpendicu- 

 lar distances or intercostal spaces are all 

 increased, and the spine is more erect. 



This experiment, therefore, demonstrates 

 two things : 1st, that by artificially inflating 

 the chest, the intercostal spaces are widened, 

 and 2dly, that the spine becomes more 

 erect. It is an experiment most unfavour- 

 able for showing these two points, because 

 the altered shape of the thorax by insufflation 

 is not to be compared with the exceedingly 

 enlarged condition produced by vital inspira- 

 tion ; in which case the spine becomes more 

 erect, and the intercostal spaces consequently 

 wider. By placing the fingers in the inter- 

 costal spaces of a living subject during 

 deep inspiration and expiration, it may easily 

 be perceived that in the former they widen, 



Fig. 681. 



Thorax artificially inflated with air. . 



and in the latter they collapse. From 3000 

 observations we have found that, in deep in- 

 spiration, the body becomes more erect, and 

 less so in expiration. 



Insufflation is not the same, in effect, as 

 inspiration. In the former we force air into 

 the chest, until the parts most yielding, as 

 the diaphragm and abdominal parietes, are 

 rendered so tense that their tension is suffi- 

 cient to overcome the elastic force of the ribs, 

 their cartilages, and the lungs ; then, and not 

 until then, do we move the costal part of 

 the thorax. On the other hand, in the living 

 and deep inspiration, we lift the ribs and 

 sternum, the most unyielding portions, first. 

 These solely produce the threatened vacuum 

 which inflates the lungs, whilst very little, if 

 any, is accomplished by the diaphragm. 



The following table shows the measure- 

 ments of the thorax, when expanded by in- 

 spiration and insufflation. 



