SKULL OF THE ^GITHOGNATHOUS BIRDS. 307 



As a stand-point for comparison, this typical Crane's palate is of the utmost import- 

 ance if the form next to be described is to be truly interpreted. 



2. Ox THE Skull of the Sun-Bittern (Eurypyga helias). 



The familiar term for this bird might serve as a text to show how completely the 

 outward observation of a bird fails, in many cases, to give a clear insight into its 

 nature. And yet this is, as it were, a Bittern-Crane ; a thin partition divides it from 

 the Bitterns, although it is not a desmognathous Pelargomorph, but a schizognathous 

 Geranomorph. 



A thorough analysis of the trunk, and, indeed, of all the rest of its body, would be 

 found to harmonize with what we see in the head. 



This bird is one of those very teaching forms which, while ascending in certain things 

 above its own family, also descends in others, and shows its close affinity to simpler 

 types ; it is at once higher and lower than a typical Crane. In the abortion of the 

 prsesphenoidal bar it comes close to Himantopus ; but that character also occurs in Pha- 

 lacrocorax amongst the Pelecanine types. This is a rare thing in the class ; for, as a 

 rule, if even the orbito-sphenoids are suppressed, the praesphenoid runs back from the 

 upper process of the perpendicular ethmoid, partly dividing the great postorbital 

 fenestra of the skull where the hemispheres and olfactory crura are tilted up and lie on 

 a shelving floor, most of which is mere membrane. 



The Pluvialine birds are very apt to have this deficiency of bone, through the abor- 

 tion of the orbito-sphenoids and arrest of the orbital plates of the frontals. Also, 

 beneath, the large optic foramina are only divided from each other by a membranous 

 band ; and, altogether, the huge size of the eyes, and their close packing towards the 

 mid line, seem to have caused this arrest of bony growth. 



In the adult Eurypi/ga there is no appearance of lateral occipital fontaneUes ; and 

 they seem to have been a mere chink in the embryo : this is at once a sign of some- 

 thing either Ealline or Ardeine. The occipital condyle (Plate LIV. fig. 7, oc. c) is also 

 largest transversely and notched as in both Gruinse and Ardeinse. The elegantly small 

 basitemporal plate {b.t) shows also its affinity to the Bitterns ; yet it agrees in form 

 with that of the Crane. As is the rule in the Geranomorphse, the basipterygoids are 

 merely represented in the adult by a small ridge. The parasphenoid is rather bulky 

 for so delicate a skull ; and the palatines do not meet beneath it : its fore end runs 

 forwards like a prow beneath the cranio-facial notch ; and this projection is lodged 

 in the bottom of the vomerine groove. The vomer itself (figs. 7-9, v) is perhaps the 

 most elegant and attenuated of any in the entire class, although it is a double bone. 

 It is much more delicate than that of the Humming-bird (Trans. Linn. Soc. ser. 2, 

 Zool. vol. i. pi. 22. fig. 3), and, strange to say, agrees witli its Trocliilian counterpart 



VOL. X. — PART VI. No. S.^Jime 1st, 1878. 2u 



