184 Dr. J. F. Halls Dally.. On-the. [Jan. 24 
examinations of healthy adults, in deep inspiration, the average antero- 
posterior range of movement was as follows :— | 
At upper aperture of thorax opposite 1st thoracic vertebra, 6 mm. | 
Midway between upper aperture of thorax and level of diaphragm opposite 
5th thoracic vertebra, 7°5 mm. 
At level of posterior part of diaphragm opposite 10th thoracic vertebra, 
9 mm. 
These measurements show that on the average the spinal column is most 
displaced towards the lower part of the thoracic curvature, and that rectifica- 
tion lessens from below upwards. Individual differences, however, are not 
infrequent. ‘This straightening, which occurs especially in that segment 
of the spine which articulates with the 6th, 7th, 8th, and 9th ribs, 
happens as a consequence of the backward push of the sternal ribs when the 
sternum is raised upwards and forwards by contraction of the cervical and 
thoracic muscles, thus bringing a larger costal are into the place previously 
occupied by a smaller one, and so increasing the antero-posterior diameter of 
the thorax. Upon the ribs assuming a position of less obliquity, the spinal 
column, being far more limited in its possible range of movement than the 
sternum, on account of its multiple attachments can only execute a fraction 
of the sternal movement. Towards the end of inspiration, as the movement of 
the sternum reaches its dynamic limit, the remainder of the force of the 
respiratory cycle is spent upon the spine, which accordingly, during the latter 
half of inspiration, shows progressive mobility. 
In the lateral oblique position the apparent movement of tbe vertebral 
column is 6 to 9 mm.; the real movement may be readily calculated by 
means of a mathematical formula. 
Importance of the Spinal Movement.—The antero-posterior enlargement of the 
thoracic cavity produced by simultaneous extension of the thoracic vertebree 
in deep breathing has an important influence upon the aeration of the apices 
of the lungs, the forward and upward movement of the thorax, together with 
backward movement of the spine, being of far greater value than the lateral 
movement in promoting free access of air. 
IIL. Anatomical Dissimilarity of the Two Halves of the Diaphragm. 
’ Anatomically the two halves of the diaphragm differ in size and shape, the 
right half being the larger and the more powerful, the reason being that this 
half has to overcome the resistance of the mass of the liver, whereas the 
stomach is much more easily compressed by the left half. Functionally, 
although the two halves of the diaphragm are of unequal size and strength, 
yet, owing to the difference in resistance on the two sides, their range of 
