156 ME. W. P. PYCRAFT ON THE MORPHOLOGY AND 



A. trunci laterale. — This occupies the whole under surface of the wing, extending 

 backwards to a point corresponding to the level of the free end of the scapula. Its 

 width is considerable. It extends dorsad, above the scapula, about I in., and ventrad, 

 below it, about 4 in. The feathers over the front and upper end of the thigh are 

 small and sparse, suggesting the formation of an apterion, thus tending to form a 

 distinct 2^teri/la femoralis as in the Neognathw. 



A. mesogastrcei. — This includes the sternal callosity, vvhich is 3| in. long and 

 2 in. wide. Immediately caudad of this callosity the space narrows to 1| in., and 

 again to about i in., which width is sustained for the rest of its length till it ceases 

 about 3 in. in front of the cloacal aperture. 



Pterylce : — 



P. cavitis. — Tlie region of the eye is surrounded by a bare space ; so also is the 

 external aperture of the ear. The rim of the aural orifice is surrounded by feathers 

 which serve to close the aperture. The throat is bare along each side of the mandible. 

 There are well-developed eyelashes. 



Pt. alan's. — The wing is eutaxial and of great size. Remiges 28. Cubitals 16. 

 Metacarpo-digitals 12 = metacarpals 7 ; addigital 1 ; mid-digitals 2 ; pre-digitals 2. 

 The arrangement of the quills and coverts in the wing of the Rhea appears to be 

 unique, at least in so far as the arrangement of the cubital remiges and the coverts 

 are concerned. The pollex only bears a claw. 



The cubital remiges are spaced about as wide apart as in the wing of a Neognathine 

 of about the same relative size, e. g. Stork or Eagle. There is one point, however, in 

 which they diflFer considerably : rows 1 to 6 do not rest, as the others, on the ulna. 

 The 1st and 6th almost reach it, the 3rd and 4th are most distant from it. They 

 seem to have been carried away by the tension of the ala membrana posterior, stretched 

 in the angle between the manus and forearm. 



The cubital remiges are rather shorter than their major coverts : those of the hand 

 are longer. This difference in length between the remiges and their major coverts is 

 probably an indication of degeneracy. It is interesting to note, in this connection, the 

 fact that in the young chick the first cubital fiight-feathers are not remiges, but major 

 coverts. 



The metacarpo-digital remiges are arranged much as in the Weognathce, but 

 somewhat farther apart, so that they tend to form pairs with their major coverts. 

 Like the cubital remiges, they are of great length, but differ therefrom in that they are 

 longer— by an inch instead of shorter by that amount— than their coverts. The 1st 

 metacarpal remex is distinctly smaller than the rest of the series : see p. 157. 



The ventral aspect of the wing is bare. 



The coverts of the dorsal aspect are arranged in obliquely transverse series, the 

 feathers of each series being piled as it were one upon another, from six to nine 



