316 Mr. P. R. Lowe on the Osteology of the 



either side is completely lost in the shield-like bony over- 

 growth which covers the proximal extremities of the nasals 

 (Ibis, 191G, text-figure 3). In the embryo, on the contrary, 

 we get no hint of this shield-like arrangement, nor of the 

 si)ongy osseous tissue which, as a fact, we know will later 

 on spread inwards to fuse in the middle line with a similar 

 bony growth derived from the other side. 



We thus find that the morphological picture presented by 

 the lacrymo-nasal region in the embryo Sheath-bill reflects 

 some primitive generalised or ancestral type, from which we 

 could well imagine that the distinctive form and shape of 

 the lacrymo-nasal region proper to the adult Oyster-catcher, 

 Sheath-bill, Crab-Plover, Skua, or Gull might easily have 

 been evolved. 



(3) Supraorbital Region. — As regards its more generalised 

 and more simple structure, all that has just been noted in 

 regard to the facial region a])plies equally to the whole supra- 

 orbital region. It presents a genei'alised condition from 

 which any of the peculiarities proper to the aberrant 

 " Plover^' forms just enumerated might well be elaborated. 

 In some respects, it is not very unlike the condition found 

 in Squatarola. The ''notch,'' for instance, just candad of 

 the lacrymals was not much more evident than it is in that 

 genus. In the adult Sheath-bill this notch is conspicuous. 

 It may or may not be connected by a bridge of bone so as to 

 form afenestrum {cf. 'Ibis,' 1916, p. 142), and the fact that 

 it is only just indicated in the embryo is what might have 

 been expected. 



As regards the supraorbital gland, this is situated along 

 quite the outer fringe of the supraorbital margin, and there 

 is no very obvious groove corresponding to it. It would 

 appear, therefore, that as the gland increases in size with 

 maturity, so the supraorbital grooves grow deeper, widei", 

 and more defined ; and this, again, goes to suggest that these 

 grooves, which are so conspicuous in the adult Sheath-bill 

 and the aberrant Plovers already referred to, have but very 

 little significance from the point of view of phylogeny. The 

 gland apparently has grown to such large proportions in 



