" QTTINTOCUBITALISM " IN THE WINK OF BIRDS. 223 



variable, nearly every condition from full formation to complete 

 absence being present. Traces of it are more common than not 

 among pigeons generally. In the eutaxic forms it is never well 

 developed. Traces of it occur in «, B, C, and D ; in tlie others, 

 as ill Passeres, it is completely absent. 



At this point, I may sum up the evidence from the muscular 

 structure of the wing in the eutaxic pigeons. They all exhibit 

 high stages in the progressive changes to be found among pigeons, 

 and in many of these changes they recall conditions to be found 

 among the Passeres. I do not for a moment wish to suggest that 

 there is any genetic relation between Pigeons and Passeres ; but 

 it appears to me that in many points the specialized pigeon-wing 

 shows convergent resemblances to the specialized wing of Passeres. 

 These convergences are peculiarly well marked among the 

 eutaxic forms. 



M. anibiens. — This muscle is one of the most interesting and 

 variable structures among birds, and it is only natui^al to find 

 that the conditions it presents among pigeons are variable and 

 significant. It is impossible to doubt that the pigeons are 

 among that great group of birds characterized by Grarrod as 

 Homalogonatae, from the normal presence in them of an ambiens 

 muscle. Among some Homalogonatous birds (as, for instance, 

 Parrots, Herons, and8torks)the ambiens may be present orabsent. 



In a former paper (5) I showed that there may be found 

 among Homalogonatous birds, apparently devoid of an ambiens, 

 distinct vestiges of the former existence of that muscle. In 

 another memoir (6) I was able to show that there occurred as 

 individual variations in Opistliocomus almost every stage in the 

 degeneration of the muscle, from complete presence to such 

 reduced vestiges as I had described in Parrots and Herons. I 

 do not think it open to doubt that the ambiens muscle is a 

 normal and ancestral constituent of the musculature of pigeons, 

 and that when it is degenerate or rudimentary or absent, such 

 conditions are secondary. In the great majority of pigeons I 

 have dissected it is present in the ordinary form. On the other 

 hand, among the eutaxic pigeons it shows marked ti-aces of 

 reduction. In F alone is it present in the complete normal 

 condition. In a and C it is present above the knee in an 

 extremely reduced form ; the usual channel through the fascia; 

 over the knee is absent and the slender tendon disappears. 

 Below the knee, and quite unconnected with the upper part, 



