512 
MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
the varying curve, a, b, c denotes the spinal column ; d, e, f the ribs represented 
as straight rods ; when the superior ribs d, articulating with the upper obliquity a, 
are raised as in D 2, inspiration, they approach each other. When those (e) hinging 
on the vertical portion of the spine are raised, they become more remote ; and still 
more distant do those (/) become that articulate with the lower obliquity. 
D 1. Expiration. D 2. Inspiration. 
This diagram is overdrawn and does not take into account the curved form of the 
ribs, their lateral thrust, the extent to which their vertebral portions are drawn 
backwards, the deepening of the dorsal arch, or the other causes that modify the 
results, but do not alter the principle demonstrated in the above figure. 
We shall find this principle run through the whole of the Mammalia. 
33. Examples in the Ass , the Sheep, the Pig, and the Dog, Plate XXVIII. fig. XI.*. 
In the Ass-|~, whose costal cartilages are unyielding and firmly united to the rib, the 
six superior ribs, which gradually lengthen, hinge from the upper curve of the dorsal 
arch ; when they are raised, they all approach nearer to each other, the lowest of them, 
from its increased length, being more raised anteriorly than the rest. The seventh 
* Drawings are deposited in the Archives of the Royal Society, showing the position of the ribs and muscles, 
when the lungs are flaccid (expiration), and when they are distended (inspiration), in the Ass (fig. X. a. b.), the 
Pig (fig. VII. a. b.), the Sheep (fig. VIII. a. b.), the Dog (fig. XI. c. d. e.f.). These figures will be referred to 
in foot-notes. 
t Fig. X. a. b. Archives of the Royal Society. 
