530 
MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
The breadth of the chest is considerably greater in proportion to its depth, and 
the mass of the upper portion of the lungs is greater relatively to the lower portion 
in Man than in the other Mammalia. The ribs descend first outwards and back- 
wards, then outwards and forwards, and finally forwards and inwards. 
During inspiration all the ribs are raised except the lowest of them ; the diaphrag- 
Diagram M. 
1. Expiration. Dorsal view. 2. Inspiration. 
matic set (see diagram M 2 , fig. XV. b.) are not raised so much as the thoracic or the 
intermediate sets. All the ribs are further apart from each other posteriorly in 
M 2, fig. XV. b. inspiration, than in M 1, fig. XV. a. expiration. 
Diagram N. 
2. Inspiration. Sternal view. 1. Expiration. 
■2 1 
Anteriorly on inspiration (diagram N 2, fig. XIII. b.), the costal cartilages, which 
articulate by moveable joints with the sternum, are raised with the ribs ; the upper 
edge of each cartilage glides towards the sternum in relation to the lower edge of 
that above it. The second cartilage approaches the first rib, while the other carti- 
lages become more remote from each other, and the angles formed by the ribs with 
the cartilages become more open. The breadth of the chest is much increased by 
