SKULL OF THE ^GITHOGNATHOUS BIRDS. 273 



The young of the Hedstsivt Suticilla, shown in the former part (pi Iv. fig. 13), and of 

 the House-Martin and Golden Oriole, given in this present paper (Plate LII. figs. 4 & 6), 

 show the primary form of the bone, which is a gently arched and pointed bar, broaden- 

 ing suddenly in its hinder thii-d, where it sends inwards to the parasphenoid two laminae, 

 an upper and a lower. These, as we have seen, are the interpalatines below and the 

 ethmo-palatines above ; opposite these twin plates a triangular flap of cartilage, the 

 transpalatine, grows backwards and outwards ; it ossifies separately, and then ankyloses 

 with the main bar. On the upper surface of the upper lamina the pointed end of the 

 pterygoid is applied ; this becomes distinct as the mesopterygoid [ms.^pg), and soon 

 ankyloses with the palatine. 



In Coccothraustes the pointed end of the pterygoid has become the steep, ribbed, skull- 

 embracing plate seen in front of the pterygoid spatula (Plate L. fig. 3, ms-inj). The long, 

 pointed, slender prsepalatine bar (figs. 1-3, jir.pa) has become prsemorse, thick, and 

 solid, and dilates from side to side as a huge buttress of bone. Behind and outside 

 this great bony foot the bone soon widens again ; for the transpalatine cartilage has 

 ossified, become ankylosed, and by copious periosteal outgrowths has grown into another 

 " foot," with thin digitiform processes. Of the hinder twin plates the lower is only one 

 third the extent of the upper ; and thus the interpalatine, becoming postpalatine, is 

 pointed in front and behind, is coiled upon itself at its inner edge, so as to make three 

 fifths of a tube. Here we fiind the palatine bones, above, tending to throw the inner 

 narial opening far backwards, as in the mammal. The hollow roof of the nasal passage, 

 which is so much enclosed behind, is of great extent ; the large, hollow ethmo-palatine 

 plates, thoroughly ankylosed to the vomer, are also completely confluent with one 

 another. This hollow roof is two-ridged ; and these ridges, formed, as we see, by the 

 mesopterygoids (fig. 3, ms.2)g), clasp the parasphenoid and the base of the orbital 

 septum, along which, in every movement of the rostrum in front, the whole pterygo- 

 palatine arcade glides. 



The pi-sepalatines articulate with the rostrum by coarse sutural teeth, which are inter- 

 mingled with a strong fibrous tissue serving as a ligament. I can find no proper arti- 

 cular cartilage, nor any trace of a synovial cavity ; the same may be said of the cranio- 

 facial hinge, above, and of the junction of the stout jugal bar with the rostrum laterally. 

 All these _/:'ye junctions are anatomically like, and like in general purpose. 



The magnificent rostrum (which, like its counterpart below, the dentary region of the 

 mandible, has no fellow in the bird class) is composed mainly of the praemaxillaries, but 

 is flanked in its hinder part, both above and below, by the maxillaries and nasals. As 

 the palatines become eroded and short in front, so are the maxillaries behind ; these lose 

 their jugal process to articulate with the jugal bone (fig. 1,/), an unusually high and 

 stout bar. 



All traces of the composition of the rostrum are gone, even above, at the "hinge ;" 

 but the maxillaries, small and inwardly placed, as in most osseous fishes, can be detected 



