48 Transactions of the 



points in the figure ; the antero-superior angle of the " periotic " 

 mass breaks out between the "squamosal" and " ali-sphenoid " 

 (sq., al. s.), and a lateral element of this organ is seen below the 

 head of the quadrate ; this latter bone (pto.) is the " pterotic," and 

 the former the " sphenotic " (P.), the symmorph of the " post- 

 frontal" of the Osseous Fish. Laterally (Plate V., Fig. 1) and 

 behind (Plate VI., Fig. 1) the "epiotic" (ep.) is well seen as an 

 oblong obliquely-placed tract of bone overlying the "posterior semi- 

 circular canal." The main part of the mass is only to be seen from 

 within, but a little of the chief bone, the "prootic" (Plate VI., 

 Fig. 2, fro.) is seen below and outside the " foramen ovale." 

 The opisthotic or fifth osseous element of the ear-mass has already 

 coalesced with the " ex-occipital," and is becoming ankylosed to the 

 prootic. In a paper which I hope will soon appear in the ' Philoso- 

 phical Transactions,' I have gone into this matter thoroughly, and 

 have shown why I have had the audacity to add two new elements 

 to the " periotic mass," namely, the " pterotic " and the " sphenotic." 

 Professor Huxley is responsible for the terms " prootic," " opis- 

 thotic," and " epiotic." My terms are in imitation of his. With 

 regard to the bone which I have called " pterotic " (See Fowl's 

 Skull, Plate 85, Figs. 1 and 4, jpfo.), it is a bony centre with 

 which I have long been familiar, but its unusually fine development 

 in the Sparrow-Hawk has at last thrown an unexpected light upon 

 certain bones in the Lizard's skull. By the light of a most patient 

 and long -continued study of the tissues microscopically — having 

 never been satisfied with rough observations, although I have not 

 used extravagantly high powers — I now (Dec. 3, 1872) can master 

 and masticate things that have been as gravel to my teeth for years 

 past. "When Professor Huxley was working out his " Malleus and 

 Incus " paper, for which all posterity shall bless him, he wrote to me 

 (Jan. 29, 1869) a letter with a sketch of the condition of the facial 

 arches in "Hatheria alias Sphenodon." 



In his graphic pen-sketch the hyoid arch is seen to be attached 

 to the side of the " auditory mass," and a piece of cartilage at the 

 end of the " par-occipital bones " is pointed to, with this description, 

 namely, "a bit of cartilage with endostosis, which some call pte- 

 rotic." This granular epiphysis anyone can see in a Lizard's skull, 

 and outside it a strongly binding falcate bone (an " ectostosis") 

 which is wedged-in between the similarly falcate squamosal and the 

 out-turned parietal horn. The two falcate bones thus overtop 

 the "quadrate," binding the cartilage to which that bone hinges, 

 like metallic clamps. The some body who had called that endosteal 

 patch "pterotic" has often foregathered with his friend as to the 

 nature of the post-squamosal " sickle "; it stood out, an enigma. 

 This is one of those points in the histological study of the meta- 

 morphosis of a bird, in its ascent above a Lizard, which is so 

 very instructive. In the bird the " pterotic " (see Plate VI., 



