On the Pterylography of the Hoatzin. 345 



XXVIII. — On the Pterylography of the Hoatzin, Opistho- 

 comus cristatus. By W. P. Pycraft, M.B.O.U., Assistant 

 to the Liuacre Professor of Comparative Anatomy, Oxford. 



(Plates IX .-XI.) 



Although several writers have recorded observations on the 

 pterylography of Opisthocomus, no one hitherto has given a 

 really complete account of the pterylosis either of the adult 

 or of the earlier stages. So far as the material which has 

 been submitted to me has permitted, I have endeavoured 

 to fill this gap, and trust I shall be found to have suc- 

 ceeded. Certain points relative to the development of the 

 neossoptiles and embryonic rhamphotheca (p. 352) are yet 

 under investigation ; but these belong rather to the province 

 of histology than pterylography, and will be treated of in a 

 future paper, together with a few details concerning certain 

 muscles which I have studied. 



My investigations have been carried on in the Depart- 

 ment of Comparative Anatomy of the Oxford University 

 Museum, and hence have been subject to the control of 

 Prof. E. Ray Lankester, to whom I wish to express my 

 thanks for grants of time from other work, and for other 

 favours. 



I propose to proceed with my description from the known 

 to the unknown, from the adult to the embryo. 



I. Pterylosis of the adult Opisthocomus. 



Pterylce : — 



Pteryla capitis (PI. IX. fig. 1, Pt.cap.). — Of the feathers 

 of this tract on the sides of the face nothing remains but a 

 few bristles, which represent the shafts of sometime feathers. 

 The eyelids are provided with eyelashes. 



Pt. colli"^ (PL IX. figs. 1-3, P^.co//.).— This is a con- 



* Usually the neck-tract is divided into a dorsal and a ventral band by 

 an apterium — the apt. colli laterale. Sometimes, by a forward extension 

 of the apterium mesogastrcei and spinale, the neck-tract is divided not 

 into a dorsal and ventral, but two lateral tracts — the pteryla colli lateralet 

 of Nitzsch. 



1 propose now to restrict the tt^rm pt. colli to those cases in which the 



