PERONEAL MUSCLES IN BIRDS. 1069 



lost the brevis altogether. The Falconifoi-mes show an interesting 

 series. Serpentarius is in quite the central position ; in Cathartce 

 the superficial origin of the longus is slightly reduced, but the 

 muscle remains the dominant of the pair. In the Falconidse 

 (omitting jPa?if^to?i) the superficial origin and the longus generally 

 tend to be reduced, but tlie anchor and slip to III always persist 

 and are strong and functional ; the brevis increases greatly and 

 may equal or surpass the longus. In so far the Falconiformes 

 present a parallel with the Owls, but are to be distinguished from 

 that group by the retention of the longus with its anchor and 

 slip. In tlie Alectoromorph Legion the great majority remain in 

 the central condition. The longus is invariably present, the 

 superficial origin is almost invariably the stronger, the anchor is 

 always present and the slip to III absent only in the Heliorni- 

 thidfe. The brevis is almost invariably the weaker muscle and 

 shows a strong tendency to disappear, e. g. among the Tinamus 

 it may be excessively feeble, it is feeble or dejgenerate in some 

 Galliform birds, absent or reduced in some Gruidte and some 

 Gharadriidse. The Oolumbae are specia.lly interesting ; the longus 

 is always present with anchor and slip to III, but there seems to 

 be a tendency for it to be reduced and for the brevis to increase, 

 especially in the smaller and most Passerine-like Pigeons, 



In theCoraciomorphine Legion the characteristic tendency is 

 for the reduction of the longus at the expense of the brevis. The 

 Orders, however, show mai^ked differences in the extent to which 

 this process has occurred. Of the Ouculiformes, the Cuckoos and 

 Plantain-eatei's remain almost in the central condition, and, 

 although the brevis is always well developed, it is surpassed by 

 the longus. The Parrots, like the Pigeons, show within the 

 group all stages from an almost central condition where the longus 

 is complete and surpasses the brevis, through stages in which the 

 longus is still well developed, although it has lost the slip to III, 

 to the final stage in which there is almost no trace of the longus 

 remaining. The Ooraciiformes have moved furthest from the 

 central condition. A very few, the Motmots, some of the King- 

 fishers, Podargus among the Caprimulgi, and Trogons and Barbets 

 show almost the central condition, but even amongst them the 

 longus is usually very little superior to the brevis, although it 

 retains its parts. In most Ooraciiformes the longus is at least 

 feeble, has usually lost its slip to III and is often entirely absent. 

 The Passeriformes, on the other hand, are remarkably constant 

 and very near the central condition, although the brevis may 

 equal or nearly surpass the longus, and in one case (Hirundo) 

 the slip to III has been lost. In the diagram reproduced as 

 text-fig. 190, I have endeavoured to show in a diagrammatic 

 fashion the general trend of the modification of the pei'oneals in 

 the groups of birds. The central space represents the central or 

 primitive condition, the area to the left the degeneration of the 

 brevis, that to the right the degeneration of the longus. The 

 placing of the named enclosures represents roughly the positioft 



Proc. Zool. Soc— 1913, No. LXXI. 71 



