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124 THE NASAL BONES OF BIRDS, 
21. ON THE VALUE IN CLASSIFICATION OF A PECU- 
LIARITY IN THE ANTERIOR MARGIN OF THE 
NASAL BONES IN CERTAIN BIRDS.* 
Since commencing the study of the anatomy of birds, it has always 
appeared to me that two distinct types of nasal bones can be dis- 
tinguished among them without difficulty—and that if those which 
present the abnormal characters are considered separately, they pre- 
sent other features in common which justify their being placed in the 
same class, and their entire separation from those which present the 
less modified arrangement. 
In most birds the anterior margin of the nasal bone is concave, 
with the two cornua directed forwards—one along the outer edge of 
the nasal splint of the premaxilla, to form the inner margin of the 
osseous external nares, whilst the other, which is free, descends as 
part of the external boundary of the same aperture in connection 
with the ascending process of the maxilla, which it joins. These two 
processes become continuous behind with the body of the bone, and 
with one another, there being no interruption of any kind between 
them. Such a condition is found in its simplest form in Otis and 
the Galline proper; and birds possessing the bone so constructed may 
be termed holorhinal: in them a transverse straight line, drawn on the 
skull from the most backward point of the external narial aperture of 
one side to that of the other, always passes in front of the posterior 
terminations of the nasal processes of the preemaxille. 
But several birds present a very different condition. In Grus, for 
example, the posterior contour of the osseous external nares, instead 
of being rounded, as in holorhinal birds, is apparently formed by the 
divergence of two straight bars of bone, which enclose an angular 
‘space between them. These two processes evidently correspond to the 
two anteriorly directed cornua of the holorhinal skull described above ; 
but they appear in many cases to be so different in density, and the outer 
one joins the body of the bone so abruptly, that it seems at first sight 
to be an independent ossification; however, I have no reason to 
believe that such is the case. As in holorhinal birds, so in those 
under consideration, which may be termed schizorhinal, the internal 
process of the nasal bone runs forwards along the outer border of the 
* “ Proceedings of the Zoological Society,” 1873, pp. 83-8. Read, Jan. 7, 1873. 
