514 
MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
behind and below. The superior (or anterior) part of the chest is narrow, the dia- 
phragm is very oblique, the diaphragmatic ribs are numerous, and their expanding 
movements great. 
In the Dog, the body of the lungs and the upper lobes are large ; they are nearly 
as long in front as behind. The base of the lung is horizontally concave ; the 
diaphragm is drawn down almost as far in front as it is behind ; the thoracic ribs are 
numerous, and have great play, at once deepening and widening the chest to a great 
extent. The diaphragmatic ribs are few in number. 
§§ 36-54. Animals that have unyielding costal cartilages — the Pig, the 
Calf (Plate XXVII. fig. IX.), the Sheep and the Ass. 
§§ 36-43. Costal Mechanism. 
§§ 36-41. Thoracic set of ribs. 
36. In the Pig* the straight costal cartilages articulate by moveable joints with the 
sternum and the sternal ribs. The seventh and eighth costal cartilages are linked 
together. During inspiration the six superior ribs are raised and drawn nearer to 
each other; the articulation with the cartilage is drawn slightly forward, and that 
with the vertebra backwards ; the sternum is pushed forwards by the cartilages 
riding on the ribs. The superior curve of the dorsal arch is increased, the attach- 
ment of each of the ribs being further back in relation to that above in inspiration 
than in expiration. The extent to which the sternum and vertebrae are pushed 
further apart is inconsiderable ; this is due to the great lateral expansion. 
3 7- The elevation of the ribs increases the depth and width of the chest. Diagrams E 1 ’ 2 , 
pi.2-3.4_ 
The diagrams E 1 and E 2 are side views, F 1 and F 2 views looking as it were down 
Diagrams. 
Expiration. 
F 3 
E 1 E 2 side views. F 1 F 2 views looking down into the chest ; a transverse section. F 3 F 4 front views. 
* Fig. VII. a. b. Archives of the Royal Society. 
