522 
MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
§§ 55-57- Animals with flexible cartilages — the Dog (Plate XXVII. fig-. X.), 
the Seal (Plate XXVI. fig. VIII.), the Rabbit (Plate XXVIII. fig. XI.), the 
Otter (Plate XXVIII. fig. XII.) and the Monkey. 
§§ 55-5 7- Costal Mechanism. 
55. The Dog, Seal, Rabbit and Monkey. — In the Dog and its allied species, the Seal 
and the Otter, and in the Rabbit and the Monkey, the costal cartilages are long, 
slender and flexibly elastic ; they are firmly fixed to the ribs, and they articulate with 
the sternum. In the Dog and the Rabbit the articulation with the sternum is by a 
horizontal chisel-end that is united to it by a ligament, and moves freely upwards and 
downwards. In the Seal and the Monkey the articulation is between a ball-and- 
socket and a hinge-joint. The flexibility and elasticity of the cartilages permit them 
to bend and spring on themselves through their whole length. They have, in relation 
to the ribs and the sternum, exactly the same function and the same principles of 
action as the sternal ribs of birds, and the straight double-hinging costal cartilages 
of the Sheep, the Calf, and the Pig. 
56. The inspiratory elevation of the ribs increases the depth and width of the chest. 
Diagrams K 1-2 , L 1-2-34 represent a rib in expiration 1-3 and inspiration 24 . KK are 
side views ; L 1 L 2 views looking down as it were into the chest, and L 34 front views. 
Diagrams. 
a transverse section. 
Expiration. Inspiration. 
In inspiration, diagram K 2 , the rib and the costal cartilage are each raised, the eleva- 
Views looking down into the chest ; 
Front views. 
1 
