1847.] BOWERBANK ON THE PTERODACTYLUS GIGANTEUS. 3 
with the published specimens, as to impress more firmly than before 
upon my mind, the conviction that the whole would ultimately prove 
to be the remains of Pterodactyls. With a view of deciding this 
question if possible, I determined upon a close microscopical examina- 
tion of the structural peculiarities of the bones, in the hope of elicit- 
ing some characters which would, in conjunction with their external 
forms, point out with some degree of certainty the class of animals to 
which these interesting remains in reality belonged. 
In the first place I removed some small fragments from the jaw 
of the Pterodactyl from the chalk, in my own possession, and im- 
mersing them in water between slips of glass, I submitted them to 
examination by transmitted light with a power of 500 linear, and I 
was at once struck by the great difference in the proportions that ex- 
isted between the bone-cells of the specimen under examination, and 
those of the human bone with which I was familiar. A measurement 
of five cells of the latter gave an average of length ,2, inch, greatest 
diameter 5,1, inch, while an average of five cells from the lower jaw 
of the Pterodactylus giganteus, represented by fig. 1. Pl. I., gave— 
length ~1. inch, greatest diameter, mch. In the latter also the 
bone-cells were considerably fewer in number, within the same amount 
of space, than they were in the human bone, and the canaliculi ra- 
diating from them less in number and larger in diameter. 
With these striking differences in structure before my eyes, I felt 
a strong hope that the comparative number and proportions of the 
cells would afford a sufficient means of discriminating between the 
remains of the Pterodactyls and those of mammals, and probably 
birds; and I determined therefore, in the first place, to examine 
microscopically the whole of the bones from the chalk, and then to 
compare the results with those which might arise from a similar in- 
vestigation of the bones of recent reptiles and birds. 
Upon submitting to examination minute fragments of all the Ptero- 
dactyl bones represented in PI. I. vol. ii. of the Geological Journal, I 
found the bone-cells in every case to agree precisely in their propor- 
tions and mode of distribution with those from the lower jaw of the 
Pterodactylus giganteus which are represented by fig. 1. Pl. I. 
I then called upon Prof. Owen and informed him of my wish to 
examine the structure of the bones described by him in the Trans- 
actions of the Geological Society as those of birds, and he kindly 
furnished me with some minute fragments from near the centre of 
the shaft of the bone, represented by fig. 1. Pl. 39. vol. vi. of the New 
Series of Transactions of the Geological Society. Upon immersing 
these in Canada balsam, and submitting them to a similar course of 
microscopical examination to that which I had before adopted, I 
found the bone-cells to possess the same small diameter and great 
elongation that characterized those from the jaw of the Pterodactyl 
and the other remains of the same animal; the average length of 
five of the cells represented in fig. 2. Pl. I. being =4,; inch, and 
the greatest diameter z1,, inch, so that in reality they are more 
elongated than those from the jaw of the Pterodactyl; but this it is 
quite natural should be the case, as I have subsequently found that 
B2 
