SKULL OF THE ^GITHOGNATHOFS BIRDS. 293 



In this species, as in the Muscicapidse of Celebes and Australia {Lalage and Pe- 

 troica, see Part I. pis. Ix. & Ixii.), and also as in the Whinchat, there are no additional 

 palatine bones (palato-maxillaries), such as we find in the Mniotiltidae 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 urhica), 1st summer. 

 Family Hirundinidae. 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 Svnfts, and not to the kind of the 

 ordinary Warblers. The Swifts, however, lie on the extreme margin of the Coraco- 

 morphae, and form another group, which leads to the Goatsuckers ; but the Swallows 

 have retained (or gained) that perfect syrinx 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 half-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. 

 pi. Iv.), as well as with the skull of the young Oriole and Flycatcher just described 

 (figs. 6 & 9). 



The cranial cavity in the adult Chelidon urhica 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 yormg 

 (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.pg) is seen to be giving ofl' its lanceolate mesopterygoid for union 

 with the palatine ; afterwards its fore end is a spatula, concave to the parasphenoid 

 [pa.s). The palatines, nader the power of the Jissirostral 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 prsepalatine point, has a large ear-shaped transpalatine 

 cartilage, rapidly ossifying, independently, by endostosis. In harmony with the wide 



2s2 



