Sternum.
To a marine animal that breathed air, it was essential to possess an apparatus whereby its ascent and descent in the water may have been easily accomplished; accordingly we find such an apparatus, constructed with prodigious strength, in the anterior paddles of the Ichthyosaurus; and in the no less extraordinary combination of bones that formed the sternal arch, or that part of the chest, on which these paddles rested. Pl. 12, Fig. 1.
It is a curious fact, that the bones composing the sternal
arch are combined nearly in the same manner as in the
Ornithorhynchus[1] of New Holland; which seeks its food
its lungs, before they descended beneath the water. In the Lond. and Edin. Phil. Mag. Oct. 1833, Mr. Faraday has noticed a method of preparing the organs of respiration in man, so as considerably to extend the time of holding the breath in an impure atmosphere; or under water, as practised by pearl-fishers; and illustrated by experiments of Sir Graves C. Houghton. If a person inspires deeply, and ceasing with his lungs full of air, holds his breath as long as he is dale, the time during which he can remain without breathing will be double, or more than double, that which he could do if he held his breath without such deep inspiration. When Mr. Brunel, jun. and Mr. Gravatt descended in a diving-bell to examine the hole where the Thames had broken into the tunnel at Rotherhithe, at the depth of about thirty feet of water, Mr. Brunel, having inspired deeply the compressed air within the diving-bell, descended into the water below the bell; and found that he could remain twice as long under water, going into it from the diving-bell, at that depth, as he could under ordinary circumstances.
Mr. Gravatt ha also informed me that he is able to dive, and remain three minutes under water, after inflating his lungs with the largest possible quantity of common air, by a succession of strong and rapid inspirations, and immediately compressing the lungs thus filled with air, by muscular exertion, and contraction of the chest, before he plunges into the water. By this compression of the lungs, the specific gravity of the body is also increased, and the descent is consequently much facilitated.
All these advantages were probably united in the mode of respiration of the Ichthyosaurus, and also in the Plesiosaurus.
- ↑ In this anomalous animal the Ornithorhynchus or Platypus, we have
