348 Dll. R. W. SHUFELDT’s MORPHOLOGICAL 
distance and upon which they are gradually lost. These riigte 
are so well marked that they may be easily discerned from an 
examination of the external surface of the stomach ; and upon 
the dorsal aspect of the organ they seem to rise into a sort of 
transverse ripple, a character present also in the Whip-poor-will. 
The oesophagus is of large calibre in these birds, and, as stated, 
thick and firm as it approaches the gastric pouch. 
The small intestiueis delicately constructed, and not especially 
large as it passes from the wall of the stomach at a point situ- 
ated at the upper right side of the organ, not far from where the 
oesophageal tube enters. 
Inside the stomach the gastric rugae are covered by a moderate 
layer of corneous tissue, composing about one third the thickness 
of the stomach-wall, which may best be seen upon a section of 
the organ. 
Of the Osteology. 
For the purposes of classification I gave in my first memoir 
on the present subject (P. Z. S. 1885) sufficiently full descrip- 
tions of the skeleton in specimens of Chordeiles and Phalceno- 
ptilus Nuttcilli for all that is required in the present connection ; 
so it will be only necessary here to make some additional remarks 
upon the skeleton as found in my specimen of Antrostomus. 
Judging from the figure of the base of the skull of the common 
European Nightjar, which I copied from Huxley and repro- 
duced in my first memoir, I should say that, osteologically, 
the American form of this bird was very much like it in that 
particular system of its anatomy ; indeed, I expect that struc- 
turally the two forms are very similar. Then, as one would 
naturally have expected, I have found, upon a mere superficial 
comparison, that osteologically the common Whip-poor-will and 
Nuttall’s Poor-will (P. NuttalU) are very much more alike than 
either of them resemble Chordeiles. In fact, it takes but a 
glance at a skeleton of a true Whip-poor-will and a Nighthawk 
to convince us at once of the marked differences that exist 
between them. As I have elsewhere said, these two genera of 
Caprimulgiue birds are separated structurally by very excellent 
characters of a nature at once recognizable. 
Figures in the plates of my first memoir, above alluded to, also 
illustrated the skull of a Chordeiles and the principal bones of 
