CRETACEOUS FORMATIONS. 83 



illustration in T. XXXII, fig. 1, a section of the very bone that directly sustains the 

 large quill-feathers in the Pelican : its parietes are only half as thin as those of the 

 anti-brachial bone of the great Pterodactyle, figured in T. XXX, fig. 1 : they are 

 thinner than those of the humerus figured in T. XXIX, fig-. 1 . 



Hunter, who had obtained some of the long bones, with thin parietes and a wide 

 cavity, from the Stonesfield Slate, has entered them in his MS. Catalogue of Fossils, as 

 the " Bones of Birds :" and perhaps no practical anatomist had had greater experience 

 in the degree of tenuity presented by the compact walls of the large air-cavities of the 

 bones in that class. Of all the modifications of the dermal system for combining extent 

 of surface with lightness of material, the expanded feather has been generally deemed 

 the consummation. Well might the eloquent Paley exclaim : — " Every feather is a 

 mechanical wonder — their disposition, all inclined backwards, the down about the stem, 

 the overlapping of their tips, their different configuration in different parts, not to 

 mention the variety of their colours, constitute a vestment for the body, so beautiful 

 and so appropriate to the life which the animal is to lead, as that, I think, we should 

 have had no conception of anything equally perfect, if we had never seen it, or can 

 imagine anything more so." It was reserved for the author of the 'Wonders of 

 Geology,' to prefer the leathern wings of the Bat and Pterodactyle as the lighter form, 

 and to discover that such a structure, as is displayed in T. XXX, fig. 4, was " a 

 most improbable one to have sustained a powerful wing of any bird." 



Let me not be supposed, however, to be concerned in excusing my own mistake. 

 I am only reducing the unamiable exaggeration of it. Above all things, in our 

 attempts to gain a prospect of an unknown world by the difficult ascent of the frag- 

 mentary-ruins of a former temple of life, we ought to note the successful efforts, as 

 well as the occasional deviations from the right track, with a clear and unprejudiced 

 glance, and record them with a strict regard to truth. 



The existence of a species of Albatross, or of any other actual genus of Bird, 

 during the period of the Middle Chalk, would be truly a wonder of Geology ; not so 

 the existence of a bird of the longipennate family. 



I still think it for the interest of science, in the present limited extent of induction 

 from microscopic evidence, to offer a warning against a too hasty and implicit con- 

 fidence in the forms and proportions of the purkingean or radiated corpuscles of bone, 

 as demonstrative of such minor groups of a class, as that of the genus Pterodactylus. 

 Such a statement as that these cells in Birds " have a breadth in proportion to their 

 length of from one to four or five ; while in Hejitiles the length exceeds the breadth 

 of ten or twelve times,"* only betrays the limited experience of the assertor. In the 

 dermal plates of the Tortoise, e. g., the average breadth of the bone-cell to its length 

 is as one to six : and single ones might be selected of greater breadth. 



* Mantell, 'Wonders, &c.,' vol. i, p. 441. 



