SKULL OF THE “GITHOGNATHOUS BIRDS. 293 
In this species, as in the Muscicapide of Celebes and Australia (Zalage and Pe- 
troica, see Part I. pls. Ix. & Ixii.), and also as in the Whinchat, there are no additional 
palatine bones (palato-maxillaries), such as we find in the Mniotiltide and their allies 
(Plate XLVIII.): here we seem to be feeling our way to morphological groupings that 
cannot be disregarded by the zoologist in his taxonomy. 
These broad-faced birds lead to those which have the face still more gaping, and 
which yet depart but little from the normal Passerine type. 
Example 66. Skull of House-Martin (Chelidon urbica), 1st summer. 
Family Hirundinide. Group Oscines. 
Habitat. Great Britain. 
In this remarkable group of tender-billed gaping Passerines, there is not, as far as I 
am aware,a single aberrant character of importance. The skull, the skeleton generally, 
the digestive and the vocal organs—all these might belong to species of the genus 
Sylvia. And yet, in minor adaptive modifications (I say minor in reference to what is 
of importance in morphology) these birds are full of modifications, and to the unscien- 
tific eye they appear to belong to the kind of the Swifts, and not to the kind of the 
ordinary Warblers. The Swifts, however, lie on the extreme margin of the Coraco- 
morphe, and form another group, which leads to the Goatsuckers; but the Swallows 
have retained (or gained) that perfect syrina which is the sign and the seal of their 
right to the title “ Oscines.” 
My observations have been made on several stages; but, for the sake of mor- 
phology, I here give the skull of a ha/f-ripe nestling (Plate LII. fig. 4), as this can be 
most easily compared with the skull of the young of the Crow and Warbler (Part I. 
pl. lv.), as well as with the skull of the young Oriole and Flycatcher just described 
(figs. 6 & 9), 
The cranial cavity in the adult Chelidon urbica and C. rustica is large and ‘broad; it 
is entirely Sylviine in all essentials. The eye-sockets are very large and well rimmed. 
In the adult the pterygoids are very long, slender, and arched outwards; in the young 
(fig. 4, pg, e.pg) they are straighter and stouter. The epipterygoid process is a mere 
_ snag at first; but in the adult it becomes an ear-shaped “trochanter.” The spatulate 
fore end (fig. 5, pg, ms.pq) is seen to be giving off its lanceolate mesopterygoid for union 
with the palatine ; afterwards its fore end is a spatula, concave to the parasphenoid 
(pa.s). ‘The palatines, under the power of the /issirostral specialization, have lost no 
normal characters. The postpalatine keels (pt.pa) are smallish and incurved; and they 
are cut away, as it were, behind, and have their free edge excavated. The flat main 
bar, gently narrowing to its prepalatine point, has a large ear-shaped transpalatine 
cartilage, rapidly ossifying, independently, by endostosis. In harmony with the wide 
282 
