MOEPHOLOGT OF OPISTHOCOMUS CEISTATUS. 71 



In this bird this nucleus of cartilage is further from the metacarpal of the 

 poUex (?n.c.i) than in most birds ; I find it nearest to that segment, to which 

 I am satisfied it belongs, in the chick of Turnix rostrata ^. In that type the 

 ventrally displaced distal carpal is phalangiform, and is of the same breadth 

 as the first metacarpal, but only two thirds as long ; it is bulbous at its radial 

 end, and is immovably articulated with its own metacarpal, which is hollowed to 

 receive it. My doubts about the nature of this nucleus are still further dissipated 

 when I consider the manner in which my own pollex is ventrally displaced adaptively. 

 This little nucleus (PI. X. figs. 2, 3, 7, d.c}) is, I doubt not, the counterpart of the 

 human " trapezium." The first metacarpal (PL X. figs. 1, 2, mc}) is nearly as wide as 

 the second, but is only one fourth its length; it has already, in its cartilaginous 

 condition, become fused with the second for a short space proximally, in a manner 

 similar to the fusion of the third distal carpal with the same large dominating segment. 

 The " trochanter" projecting from the short, confluent metacarpal, shows some signs of 

 a marginal addition (see Fowl's Wing, pis. 62-64, mc") ; this is the part from which 

 the main spur grows in certain birds. The proximal phalanx of the pollex {dg}) is 

 three-fourths the thickness, and two-thirds the length, of the huge metacarpal joint 

 behind it [inc.') ; for half its length in the middle it is ossified ; its metacarpal does not 

 ossify until near the time of hatching. The distal or ungual phalanx is relatively 

 larger than the proximal ; it is very little less than that of the second digit {dg.^) ; that 

 measured with the claw on is 2'5 millim. long ; this, of the pollex, is 2 millim. ; the tip 

 of this distal joint is beginning to ossify. 



If the manus in this stage be measured from the top of the second distal carpal, it 

 will be found that the pollex is more than half the length of the huge index {dg}, 

 dg?) ; the one is 6'5 millim. long, the other 12-5 millim. On the other side of the 

 Class, in the Macrochires, in the adult state, the abortion of the pollex, with its small 

 quills forming the alula, is very remarkable, as the following instances will show : — 



Gypselus affinis . 

 CJuvtura caudacuta 

 Topaza pella . . 

 Patagona gigas . . 



Thus, instead of the first finger being more than half the length of the second, this 

 latter is, in these cases, taking the average, four and a half times as long as the aborted 



' From Formosa, the gift to me, many j-ears since, of the late Consul Swinhoe. The skull of one of these 

 valuable chicks has already been described by me in these Transactions (vol. ix. pi. liv.) ; the sternum and 

 shoulder-girdle were also described in my work on those parts, and figures and descriptions of the remainder 

 of the skeleton wUl soon be published. 



