+ PROCEEDINGS OF THE GEOLOGICAL society. [June 9, 
the bone-cells vary slightly in their proportions in different parts 
even in the same bone; those of the cancellated portions toward the 
ends of the bone being somewhat shorter and more irregular in their 
proportions than those of the shaft, surrounding the Haversian ca- 
nals, which have proved in all the specimens I have examined to be 
very nearly uniform in their size and proportions. I have therefore 
in all cases described in this paper, selected the specimens for exami- 
nation and figuring as nearly as possible from the central portion of 
the shaft of the bone. 
The result of these examinations strongly impressed upon my mind 
the conviction, that the bones described as those of birds in truth be- 
longed to Pterodactyls, and it remained only to examme and compare 
with them the structure of the bone of an Albatros; with the view of 
procuring which, I called on my friend Mr. John Quekett of the Royal 
College of Surgeons, and upon mentioning to him the course of inves- 
tigation which I was pursuing, he at once told me that he had been 
for some time engaged in an examination of the structural peculiarities 
of the bones of the four great classes of the animal kingdom, and that 
he believed that distinctive characters existed which would readily 
enable an anatomist to decide from a fragment, to which of these 
classes a bone submitted to his examination might belong. Upon | 
this declaration I immediately submitted to him Camera lucida draw- 
ings of the bone-cells from the jaw of the Pterodactylus giganteus 
from the chalk, and those from the bone belonging to the Earl of 
Enniskillen and described by Prof. Owen (fig. 1. Pl. 39. vol. vi. Geol. 
Trans. 2nd Series), and he at once declared that they were charac- 
teristic of the reptilian tribe. 
This confirmation of the opimion I entertained of the reptilian cha- 
racter of the bones under examination was the more yaluable, as 
neither Mr. Quekett nor myself were previously aware of the course 
of investigation which each had been pursuing. 
Having obtamed a portion of the shaft of a humerus of an Albatros, 
I submitted it to examination in the manner pursued with the Ptero- 
dactyl bones. I found that the bone-cells were nearly analogous in 
their proportions to those of the generality of mammals, but somewhat 
more numerous within the same amount of space, and like the mam- 
malian cells, the canaliculi radiating from them were very much finer 
and more numerous than those radiating from the reptilian bone-cells, 
either of the Pterodactylus, or of the common frog or boa-constrictor. 
The average measurement of five of the bone-cells of the Albatros, 
- represented by fig. 3. Pl. I., was—length <1, inch, greatest diameter 
zizz Inch; while those from Lord Enniskillen’s specimen were— 
length ~1. inch, greatest diameter ,;4, mch; thus exhibiting an 
essential difference in their size and proportions as well as im the 
number contained within the same amount of space and in the num- 
ber and proportions of the canaliculi radiating from the cells. 
These differences in structure and proportion I found to prevail 
equally between the bone-cells of the common frog, the boa-con- 
strictor, Paleophis Toliapicus, and other recent and fossil reptiles, and 
those of the bones of the domestic goose, duck, fowls, and several 
