AND DEVELOPMENT OF THE BIRD'S SKULL. 135 



respects, the most specialized skull to be seen amongst the Raptores. The broad foot of 

 the vomer (Plate XXV. fig. 5, v) fits like a keystone between the large maxillo-palatine 

 slabs (mxp) ; and these are bound, externally, by the dentary plate and angle of the pre- 

 maxillaries (dpx). In front of the vomer (Plate XXIV. fig. 4) the maxillo-palatine plates 

 meet, and afterwards coalesce. Ultimately, when all these structures, without and 

 within, have coalesced by extended ossification, all but the vomerine undersetter, then 

 the lateral halves of the face are indissolubly bound together, and form a structure most 

 compact and strong. 



On the Structure of the Skull in the Sparrow- Hawk (Accipiter nisus)*. 



In greater feebleness of general structure the skull of this type is intermediate between 

 that of the Falcon and the Cariama ; but the leanings of the Hawk are not so much 

 towards the latter as in the direction of that gigantic Vulturine Harrier the Secretary 

 Bird ( Gypogeranus) . The skull of a partially fledged nestling yielded the results given 

 in Plate XXV. figs. 7 & 8. Here we see at once things that agree better with the skull 

 of the Cariama, and also things that are less in conformity with it than those just 

 described in the Palcon : whilst the Cariama agrees with the Falcons, Eagles, and the 

 more Aquiline types of Vultures in having the basipterygoids early arrested, the 

 Sparrow-Hawk shows them as strong short spurs in the young (Plate XXV. fig. 7, bpg), 

 and retains them as mammillary elevations in the adult. They are still more develope'd 

 in the Harrier (Circus), more still in the Brahmany Kite (Haliastur indus), and perfectly 

 functional in the Secretary. In Accipiter the parasphenoid (pas) is stout, and bevelled 

 on each side by the under-gliding pterygo-palatines. The next median splint, the vomer 

 (v), is truly azygous, and is a long knife-blade at present ; in the young it is neither bi- 

 dentate behind nor pedate in front ; it alters but little afterwards, and agrees in this 

 respect with the whole Accipitrine division of the group. 



The desmognathism is perfect, although, in the young bird, it is " imperfectly direct," 

 as in the adult Cariama. Already the septum nasi is fast fusing with the solid fore end 

 of the premaxillaries ; and, behind, its nerve-bridges and connexion with the alas nasi 

 make it a fit wedge to fill up the space in front between the large lunate maxillo- 

 palatines (mxp), which, lying back to back, of necessity leave an open space in front for 

 the septum, and behind for the vomer. The premaxillaries form a less solid mass than 

 in the Palcon ; but this type is much more orthognathous than the Cariama. "Whilst the 

 Hawk agrees with the gallinaceous types in having a truly azygous vomer, it differs from 

 them, and is in harmony with the huge groups of the Passerines and Pluvialines, in having 

 a large mesopterygoid wedge differentiated from the fore end of the proper pterygoid (figs. 

 7 & 8, mspg, pg). As usual, the transpalatine (tpa) is rounded off, more developed than 

 in the Pluvialine types, but less than in the Passerines. The ethmo-palatine plates (epa) 

 are thin, curved, pointed laminae, embracing the head of the vomer ; the interpalatine 

 ridge (ipa) has no free spur. The prepalatine bars (prpa) reach as far forwards, or 

 nearly, as the trabecular axis of the premaxillaries ; they are thin laths of bone. 



• * For further details on this type of skull, see M. Micr. Journ. 1873, plates v. & vi. pp. 45-50. In these plates., 

 for ep read op. 



