228 FLYING SAURIANS. 
find the number of joints regularly increased by 
the addition of one, as we proceed from the first 
finger, or thumb, which has two joints, to the 
third, in which there are four ; this is precisely 
the numerical arrangement which takes place in 
the three first fingers of the hand of the Ptero- 
dactyle; (PI. 22, c. d. e. n. o. Figs. 30—38.) 
thus far the three first fingers of the fossil 
reptile agree in structure with those of the fore- 
foot of living Lizards ; but as the hand of the 
Pterodactyle was to be converted into an organ 
of flight, the joints of the fourth, or fifth linger 
were lengthened, to become expansors of a 
membranous wing.* 
* Thus in the P. Longirostris (PL 21, 39—42.) and P. Bre- 
virostris, (PI. 22, Fig-. O, 39 — 42,) the fourth finger is stated by 
Cuvier to have four elongated joints, and the fifth or ungual joint 
to be omitted, as its presence is unnecessary. In the P. Crassi- 
rostris, according to Goldfuss (PI. 22, Figs, a, m,) this claw is 
present upon the fourth finger, (43) which thus has five bones, 
and the fifth finger is elongated to carry the wing. Throughout 
all these arrangements in the fore-foot, the normal numbers of 
the type of Lizards are maintained. 
If, as appears from the specimen engraved by Goldfuss, of 
P. Crassirostris, (PI. 22, n, 44, 45,) the fifth finger was elon- 
gated to expand the wing, we should infer from the normal 
number of joints in the fifth finger of Lizards being only three, 
that this wing finger had but three joints. In the fossil itself 
the two first joints only are preserved, so that his conjectural 
addition of a fourth joint to the fifth finger, in the resto^'ed 
figure, (PI. 22, a, 47,) seems inconsistent with the analogies, 
that pervade the structure of this, and of every other species of 
Pterodactyle, as described by Cuvier. 
