226 FLYING SAURIANS. 
with those of Bats (PL 21, and PI. 22, M.) shows 
that the fossil animals in question cannot be re- 
ferred to that family of flying Mammalia. 
The vertebrae of the neck are much elongated, 
and are six or seven only in number, whereas 
they vary from nine to twenty-three in birds.* 
In birds the vertebrae of the back also vary 
from seven to eleven, whilst in the Pterodactyles 
there are nearly twenty ; the ribs of the Ptero- 
dactyles are thin and thread-shaped, like those 
of Lizards, those of birds are flat and broad, 
with a still broader recurrent apophysis, peculiar 
to them. In the foot of birds, the metatarsal 
bones are consolidated into one : in the Ptero- 
dactyles all the metatarsal bones are distinct; 
the bones of the pelvis also differ widely from 
those of a bird, and resemble those of a Lizard ; 
* In one species of Pterodactyle, viz. the P. macronyx, 
Geol. Trans, n. s. V. iii. pi. 27, page 220, from the lias at Lyme 
Regis, there is an unusual provision for giving support and 
movement to a large head at the extremity of a long neck, by 
the occurrence of bony tendons running parallel to the cervical 
vertebrae, like the tendons that pass along the back of the 
Pigmy Musk (Moschus pygmseus,) and of many birds. This 
provision does not occur in any modern Lizards, whose necks are 
short, and require no such aid to support the head. In the 
compensation which these tendons afforded for the weakness 
arising from the elongation of the neck, we have an example of 
the same mechanism in an extinct order of the most antient 
reptiles, which is still applied to strengthen other parts of the 
vertebral column, in a few existing species of mammalia and 
birds. 
