72 PEOF. W. K. PAEKEE ON THE 



first digit ; the disproportion is greater in the Humming-birds than in the Swifts. I 

 must now notice a remarkable structure. The manner in which the ectosteal sheath 

 of the second metacarpal passes along the ulnar side of the first (PL X. figs. 1-7, 

 mc.^ 7nc}) is repeated on a smaller scale in the pollex, while at the radial margin of 

 the top of the proximal phalanx there is a rounded flap of cartilage which runs 

 forwards in a sharp wedge ending in ligamentous fibres at the middle of the joint. 

 Besides this, in all these embryonic stages there is a wedge-shaped mass of inter- 

 articular cartilage (i.a.c.), which, solid and definite as it is, only remains for a time ; in 

 the adult (figs. 8, 9, dg?) it is reduced to a mere film. That these structures belong to 

 a veritable " prepollex " I have no doubt ; they are not the only cartilaginous tracts 

 on the radial side of the manus to be seen in Birds, as I shall show in another paper. 

 The mdew (dg.'^) is greatly overgro^vn ; but for that the pollex would be seen to be quite 

 normally developed as compared with tliat of an average Eeptile. The phalanges have 

 undergone the same degree of ossification as those of the pollex, and moreover its 

 metacarpal (mc.^) is ossified in an equal degree ; its distal phalanx has also the tip 

 ossified even in the 1st stage, as in the pollex. The metacarpus is twice as long as 

 the proximal phalanx, and it is one sixth longer than the second and third. That 

 third phalanx is generally lost, often suppressed, in Birds ; here it has its most 

 remarkable development, and is but little less than that of the second digit in the foot 

 (PL VII.). This digit is not siniple ; it has been complicated by intercalary or 

 secondary structures ; which, however, are not peculiar to this bird, but are very 

 common in the Carinatse. These are, first, a tract of cartilage on the extensor face of 

 the wrist, which creeps down between the head of the second and third metacarpals 

 (PL X. figs. 1, 6, mc.^'} ; this breaks out at the top of the interosseous space into a 

 bead-like swelling, which in Gallinaceous birds {op. cif. pis. 62-64, mc.^'), in Passerines, 

 and in some of their Caculine allies, grows into a large flat plate, which bridges 

 over the proximal end of that space. Below, on the ulnar edge of the proximal 

 phalanx of this great digit {dg.% there is a lanceolate tract of newer cartilage that 

 receives its bony matter from the phalanx, and this becomes a mere flange to that joint, 

 broadening it for the insertion of the " primaries ;" this part has its own osseous centre 

 in the Raptores. I look upon this structure as a sort of bifurcation, like that which is 

 so often seen in the roughly finished cheiropterygium of the Ichthyosaurs. 



The starved third digit (dg.^) has its slender metacarpal (mc.^) separated from the 

 second by a large lanceolate interosseous space ; proximally it begins much lower 

 down than tlte second ; it is continued a little further below ; it is largely ossified. The 

 phalanges of the third digit {dgS') are in a curiously-aborted condition ; there is an 

 attempt at segmentation into what should be, according to the Eeptilian norma, four 

 phalanges. In the 1st stage (PL X. fig. 1) there is one cartilaginous tract two-thirds 

 the length and half the breadth of the proximal phalanx of the second digit ; the end 

 of this tract is raised and hooked, and is, indeed, a semi-segmented ungual phalanx. 



