Anatomy of the Houtzin. 287 



lu the first place the line in Nitzsch's figure indicating the 

 position of the carina stcrni is misleading^ as it does not show 

 where the carina sterni really is ; the point is better illustrated 

 in Mr. J. Beswick Perrin^s account of the myology of Opistho- 

 comus^. Mr. Perrin does not, in this paper, enter into any 

 description of the pterylosis, but repeats Nitzseh^s figures f, 

 with the remark that in his specimens " the pterylography 

 . . . was almost identical with that figured in Nitzsch^s work." 

 The word " almost," in a question relating to pterylography, 

 allows a considerable latitude for variation ; the differences 

 in arrangement in the feather-tracts being often very in- 

 conspicuous, although very constant and therefore of im- 

 portance. 



In the adult bird the pterylosis of the head and neck is, as 

 Nitzsch has correctly stated,, continuous ; on the ventral side 

 the two ventral tracts do not divide so early as is represented 

 in Nitzsch's diagram ; the ventral surface is covered with a 

 continuous feather-tract as far down as about halfway be- 

 tween the fore and hind limbs ; after this there is a median 

 bare space of some extent, which is, however, sparsely fea- 

 thered ; the median apterion does not, in fact, commence 

 until the carina sterni, and is here exceedingly narrow, its 

 width being precisely that of the carina ; the apterion is 

 sharply marked here by a straight row of feathers on each 

 side ; from this point the apterion is conspicuous and of some 

 breadth, and the two ventral tracts become narrow, though 

 connected by scattered feathering with the femoral tracts. 



The lateral ventral tracts unite with one another some way 

 in front of the cloacal aperture. 



The spinal tracts do not show quite so regular an apterion 

 as in Nitzsch's figures ; indeed, the dorsal surface is sparsely 

 feathered all over, with stronger feathers here and there, 

 particularly anteriorly, where they form a strong band, as 

 figured by Nitzsch. 



The humeral tracts are conspicuous, as figured by Nitzsch. 



* " On the Myology oiOpisthocomus cristafus" Traus. Zool. Soc. vol, ix. 

 p, 353, pi. Ixiii. tig. 3, tb. 

 t Loc. cit. pi. Ixiii. figs. 1, 2. 



