362 
DE. E. W. SHUFELDT’S MOEPHOLOGICAL 
of the other skulls of the Hirundinidce. This is principally due 
to the fact that in the skull of Tachycineta the base of the osseous 
superior inaudible is not nearly so broad iu comparison as it is 
among the other Swallows, and consequently more nearly ap- 
proaches in appearance the skull of some of those Passeres which 
possess mandibles with rather broad bases. 
The structural details seen at the base of the skull in Tachy- 
cineta thalassina I have already shown in a previous memoir, 
wherein I have figured those parts in a specimen of that Swallow 
(P. Z. S. 1885, p. 899, fig. P); and as that figure is readily acces- 
sible to the reader, a comparison of it with the figures in the 
present paper may be made without difficulty. 
Nothing worthy of special record is to be fouud in the man- 
dible , nor in the hyoid arches of the skulls or the latter apparatus 
in the genus Tachycineta ; they present all the true characteris- 
tics of those parts as already described above with sufficient fulness 
for the Hirundinidce generally, and our present purpose. 
What I have just said of the skulls and associated parts as found 
in the two species of the genus Tachycineta applies with equal 
truth to the corresponding structures as fouud in Clivicola riparia 
and in Stelyidopteryx serripennis , of which I have several examples 
of each before me. 
In their general form they, too, remind us more of the skulls 
of certain other types of Oscines than do the skulls of the other 
Swallows which were described above, previous to our taking up 
the skulls of the genus Tachycineta. 
Of the remainder of the Axial Skeleton in the Hirundinidce . — 
My labour is considerably lightened here from the fact that I 
have already touched with some degree of fulness upon the axial 
skeleton of Tachycineta in m 3 " first memoir in the ‘ Proceedings 
of the Zoological Society ’ (1885, p. 906); and then, again, the 
sternum and shoulder-girdle of the Swallows is very well known, 
making any detailed account of it here unnecessary. 
By those who have read it, it may be remembered that 1 found 
35 vertebrae and a pygostyle in the spinal column of a Swift (JMi- 
cropus), and the same number of segments in the column of a 
Swallow ( Tachycineta ). Upon careful examination I am now 
enabled to state that this is the normal number for all our 
Swallows, and I have yet to find an exception to it. Should such 
an exception be found, I predict it will simply be a free, and 
