150 MR. W. K. PARKER ON THE STRUCTURE 



Tinamous," Trans. Zool. Soc. vol. v. plate xxxvii. figs. 1-5, for views of the skull of 

 Vanellus cristatus, useful for the whole comparison between the Larine and. Pluvialine 

 skulls.) 



The solid part of the premaxillaries is short. The maxillary widens at its middle, to 

 form the elegant spoon-shaped maxillo-palatine process (mxp), which is obliquely placed, 

 and has its " bowl " outside. The rest of that bone and tbe two pairs- of jugals (J, qj) 

 are very slender spicules of bone. 



The vomer (Plate XXVII. figs. 9 & 9a, v) has the form so common in Pluvialine, Gruine, 

 Ralline, Alcine, and Ardeine types ; it is formed of two lanceolate centres that unite for 

 their anterior two thirds by a sharpish angle. They become carinate below, and the 

 carina is, in the young bird (fig. 9a), divided into two tracts. These afterwards are joined 

 by fresh bone into one keel, which forks where the bone forks to form the crura that 

 unite with the under surface of that part of the palatine which was the distinct meso- 

 pterygoid bone. 



The very pluvialine mandible (fig. 7, d, af) has still a suture where the anterior and 

 posterior parts unite ; there is also an oval fenestra in front of the hinge. 



Skull of Gavia ridibunda. Qth stage. 



In the skull of the oldest specimen I have examined of this species the occipital 

 fenestrse and the basipterygoids are entirely gone. The bone is light and thin, but 

 rather dense; scarcely a trace of suture is to be seen— for instance, only above the 

 cranio-facial hinge. The only bones free are the vomer, the quadrates, and the mandible. 

 The latter bone has its sutures between the dentary and the hinder part persistent. 



The nasal capsules are only ossified in the olfactory region (aliethmoid and pars plana) ; 

 the vestibular cartilages remain soft, viz. the aliseptal with its inferior turbinal, and the 

 alinasal with its turbinal. 



But there is a structure of intense interest attached to the outturned end of the pars 

 plana, and not differentiated from it in the cartilaginous state ; this is the " os uncinatum" 

 (Plate XXVII. fig. 11, ou). This is a small triangular wedge of bone which rests upon 

 the zygoma. It is well shown in the Albatross (Diomedea). I have lately described it in 

 Dicholophus ; traces of it occur in Alca torda and TJria troile ; but its highest development 

 is found in certain arboreal birds — Plantain-eaters, Parrots, &c. 



This bone is the ethrno- palatine, or joining-piece between the trabecula and palatine 

 in front, and belongs to the same category as the basipterygoid. 



On the roof of the skull large and elegant fossae exist, on which lie the long, tongue- 

 shaped supraorbital or nasal glands. In old birds the two long ceratohyals are only 

 soft at their apex or ventral extremity ; they ossify to a great extent, ankylose in the fore 

 part, then are somewhat bowed out apart, and then come close together in front of 

 the basihyal. This latter bone sends osseous matter into more than the front half of 

 the urohyal. The lower thyrohyals are ossified. The upper and more slender pieces 

 are half soft below and at the upper ends. 



But little difference would be found between this bird in its development and the 



