MR. W. K. PARKER ON THE OSTEOLOGY OF BALiENICEPS REX. 309 



they are mere flattened styles, just expanding at their distal extremities to send 

 upwards and inwards a thin orbital plate ; so that in these birds there is nothing 

 startling in the idea of their being the ribs (pleurapophyses) of the nasal vertebra ; nor 

 would it be difficult, were we looking for cranial vertebrae, to suppose that the small 

 simple bones (the pterygoids) attached to them behind were their appendages. 



Pterygoid. (PI. LXV. figs. \ &7pg.) 



The pterygoid of the Balaeniceps is nearly an inch long, flat in the middle, clubbed at 

 both ends, carinate above, and thicker and more rounded below, especially at the distal 

 end ; whilst the proximal end is marked with three ridges, one outside, one inside, and one 

 beneath. The inside of the pterygoid, which is altogether the most concave, is scooped 

 with three cavities, one in the middle, and one at each end ; they communicate with 

 pneumatic passages. The outer part of the proximal end has a slightly convex oblong 

 condyle ; the inner has three large and some smaller teeth, which fit into the end of the 

 palatines. The distal end is obliquely scooped on its outside to form a shallow cup to 

 articulate with the convexity of the os quadratum. Above this cup are some pneumatic 

 holes, and above them a small spur, looking forwards. Synovial cartilage covers the 

 oblong condyle at the proximal end, and lines the concavity at the distal, creeping on 

 to the end of the bone. This small, oblong, thinnish, but really strong bone commu- 

 nicates the motion of the quadratum to the palatines, as the zygoma does to the pre- 

 maxillaries. Were the same bone in the Heron magnified twice its size, it would be 

 scarcely distinguishable from that of the Balaeniceps. The pterygoids are almost ossified 

 by the eleventh day of incubation in the Chick. 



Os quadratum. (PL LXV. figs. 1, 3, 6 & 7 5.) 



The OS quadratum of the Balaeniceps is a large, strong, quadrate bone, its upper 

 side being 1^ inch in extent, its posterior the same, its anterior f inch, and the in- 

 ferior side, measured in a straight line across the condyles that fit into the lower jaw, 

 1 J inch. The large upper condyloid processes are 1 inch across ; the outer appears 

 externally, articulating with the squamosal, whilst the inner passes inwards and some- 

 what backwards, and partly encroaches on the par- and ex-occipitals. These upper 

 condyloid processes are not, like the lower, completely covered with articular cartilage ; 

 for the cellular nature of the squamosal, petrosal, and occipital at this part allows 

 ihem to touch the bone only at certain points, these more projecting parts being alone 

 covered with articular cartilage : hence the discontinuity of that tissue on the head of 

 the quadratum. The upper margin of the quadratum is sharp-edged and gently concave 

 in outline ; it expands a little at the anterior end to form the crescentic tip of the orbital 

 process, which is a quarter of an inch across at its enlarged end. This orbital process 



VOL. IV. PART VII. 2 X 



