384 NOTES ON birds' sterna and skulls. 



A lacLiymal bone has, in eaoli instance, almost couiplett-ly ancliylosed 

 with the frontal and nasal of the same side ; and at the lower extremity 

 of this bone we find an ossicle similar in every respect with the one I 

 described above as occnrring- in the skull of Lams aryentatus. This 

 little bone shows well in the hgure, extending backwards from the lower 

 expanded portion of the lacrymal. 



Both of these skulls have a foramen on either side of the supra-occip- 

 ital prominence, the pair being- much larger in the large skull than 

 they are in the other. I have elsewhere pointed out that these ai)er- 

 tures may exist as extensive vacuities, or be altogether absent in the 

 same species of Duck or Goose. 



They constitute by no means a constant character for the same species 

 of any of the group, so far as my observations go ; and, indeed, in the 

 same skull the foramen may be present on one side and absent on the 



other. 



The pterygoids and the basipterygoidal facets are here, as we find 

 tliem among the anserine birds generally, and the articulation of the 

 heads of the former with the proximal ends of the palatines fire the 



same. 



As in the members of its group, too, we find the vomer to be an oblong 

 lamina of bone placed vertically, with its forward projecting spine, 

 from the antero-superior angle, resting on the osseous median mass 

 representing the fused maxillo palatine elements in front of it. 



The sl-ull* sternum* and shoulder girdle* of Ardea htrodlas.—V \^on 

 comparing these specimens with the corresponding parts of the skeleton, 

 taken from Blue Herons that I have collected in different localities 

 throughout the United States, I find little or no difference worthy of 

 mention existing among them. Length of mandibles is apt to vary a 

 little, but I take it that this is due to the age of the specimen. 



The sicull, sternum, and shoulder giruie of Nycticorajo nycticorax ncc- 



dnus. A skeleton of this Heron was not at hand at the time I completed 



my work upon the osteology of birds &c., but from an examination of 

 the skeleton of JS^ycticorax violaceiis I was rather inclined to believe that 

 we would, be enabled to pick out certain characters that would distin- 

 guish the diurnal from the more typical Night Herons. Upon making a 

 critical comparison, however, between the skull, sternum, and shoulder 

 girdle of this Black-crowned Night Heron and the same parts before us 

 in A. herodias, I fail to find any definite characters to satisfactorily dis- 

 tinguish them by, except their difference in size. Indeed, the skull of 

 the Black-crowned Night Heron agrees.in all essential details with the 

 skull as we find it in the Great Blue Heron, except, as I say, it is about 

 one-fifth less in point of size. No, if we are to look to the morphology 

 of the Herons for characters to differentiate the two American genera, 

 Ardea and Nycticorax, we, I feel sure, will have to resort to an examina- 



