180 MARINE SAURIANS. 
The ribs of the right side were united to those 
of the left, by inteiinediate bones, analogous to 
the cartilaginous intermediate and sternal por- 
tions of the ribs in Crocodiles ; and to the bones 
which, in the Plesiosaurus, form what Mr. Co- 
nybeare has called the sterno-costal arcs. (See 
PL 17.) This structure was probably subser- 
vient to the purpose of introducing to their 
bodies an unusual quantity of air ; the animal by 
this means being enabled to remain long beneath 
the water, without rising to the surface for the 
purpose of breathing.* 
* The sterno-costal ribs probably formed part of a condensing 
apparatus, which gave these animals the power of compressing 
the air within 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 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 
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. Brunei, having inspired deeply the com- 
pressed 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 
