MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
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6. On inspiration ; the ribs are raised, move forwards, glide on each other, move farther 
apart. Diagrams A 1.2. 
In diagram A 1 the ribs are depressed at their free ends as in the state of expira- 
tion. 
In diagram A 2 they are raised as in the state of inspiration. 
V. indicates the spinal column. 
b. c. d. e. the ribs, their free ends. 
b'. c'. d!. e'. the vertebral ends of the ribs. 
When the ribs are raised the free ends move forwards so as to be more distant from 
the vertebrae ; the result is, the chest is deepened. The various ribs b. c. d. e. are more 
distant from each other in fig. A 1, inspiration, than in fig. A 2, expiration. 
In fig. A 1, expiration, the free end of the rib c is considerably in front of a line b. 3, 
drawn at right angles to the rib b. In fig. A 2, inspiration, the free end of c is very 
little in front of such line b . 3 ; it follows that the lower edge of the superior rib b 
glides forward in relation to the upper edge of the inferior rib c ; and vice versd, the 
upper edge of the lower rib c glides backwards in relation to the lower edge of the 
upper rib b. 
7- The levatores costarum and external intercostals are inspiratory . Diagram A 2. 
It is evident that the line 1 representing the levator costae is much shorter in 
diagram A 2, inspiration, than in diagram A 1, expiration ; it is also evident that the 
lines 2.2.2 representing the external intercostals, which descend obliquely forwards. 
