sternum resembles that of the orhithorhynclius paradoxus . 27 
the great pectoral muscle, going from the first bone of the, 
sternum to the first bone of the pectoral fin, and a small one 
under it which may be called the small pectoral muscle ; but 
two large muscles, which have their origin from the flat bones 
and go to the first bone of the pectoral fin, or os humeri, and are 
inserted just below its head, that part being unusually broad, 
to allow of sufficient surface for their attachment. These 
muscles must be considered as peculiar to those animals that 
have this particular form of sternum. 
As these muscles probably belonged to the animal whose 
fossil bones are under consideration, as well as to the orni- 
thorhynchus, I have given them a particular description. 
Till the sternum was discovered, it could not be ascer- 
tained in what manner the animal breathed; and the ribs 
being attached to the middle part of the vertebrae, as in 
fishes, made me lean to the opinion that it breathed water ; 
but I now find, on more attentive consideration, that there is 
a difference between the mode of attachment of the ribs in 
this animal and in fishes, which admits of their having the 
motion of elevation and depression required in breathing 
air. In fishes, the attachment is single ; but here, as is 
shown in the engravings in a former paper, it is double ; 
and the two are considerably apart, as in the bird. Till it 
was determined whether the animal breathed air or water, 
little attention was paid to the nostrils, further than to find 
their place on the skull ; more particularly as in the only 
head I had seen, the bony scales of the opposite eye had 
been pushed through an aperture situated where I con- 
sidered the opening of the nostril must have been: but I 
