ICHTHYOSAURUS. 
181 
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 Ichthyo- 
saurus ; and in the no less extraordinary com- 
bination of bones that formed the sternal arch, 
or that part of the chest, on which these pad- 
dles 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 at the bot- 
tom of lakes and rivers, and is obliged, like the 
the largest possible quantity of common air, by a succession of 
strong and rapid inspirations, and immediately compressing the 
lunp tlms filled with air, by muscular exertion, and contraction 
ot the chest, before he plunges into the water. By this compres- 
sion of the lungs, the specific gravity of the body is also in- 
creased, and the descent is consequently much facilitated. 
All these advantages were probably united in the mode of re- 
spiration of the Ichthyosaurus, and also in the Plesiosaurus. 
In this anomalous animal the Ornithorhynchus or Platypus, 
we hpe a quadruped clothed with fur, having a bill like a duck, 
our webbed feet, suckling its young, and most probably ovo- 
^viparous : the male is furnished with spurs.— See Mr. R. Owen’s 
apers on the Ornithorhynchus Paradoxus, in the Phil. Trans. 
p°"“on, 1832, Part II. and 1834, Part II. See also Mr. O wen’s 
183^*^ ™ stitne subject in Trans. Zool. Soc. Lend. Part III. 
) in which he points out many approximations in the gene- 
ative and other systems of this animal to the organization of 
'■fiptiles. 
