142 MARINE SAUUIANS. 



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. PI. 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* of New Holland; which seeks its food 



before they descended beneath tlie 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 holdings 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 in- 

 spires deeply, and ceasing with his lungs full of air, holds his breath as long 

 as he is able, 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. Brunei, jun. and Mr, Gravatt 

 descended into 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, Brunei, 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 has also informed me that he is able to dive and remain three 

 minutes under water, after inflating his lungs with the largest possible quan- 

 tityof common air, by a succession of strong and rapid inspirations, and im- 

 mediately 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 havo 



