1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 289 



ledge of rneinbrano-cartilage, which reminds one of the horizontal por- 

 tion of the true lacrymal bone in certain gallinaceous birds, as the Per- 

 dicince, for example. This feature has been studied by me in Sula brew- 

 steri and 8. gossi, specimens of which I am indebted to Mr. E. J. Eeed 

 of Guaymas, Mexico, who kindly collected them for me. This mem- 

 brano-cartilaginous process probably never ossifies in the Sulidce. 



In the adult bird it is impossible to distinguish the exact position, or 

 any of the borders, of the nasal bone. 



The maxillo jugal bar shows very plainly the suture between the jugal 

 and quadrato-jugal; the latter is much smaller than the other portion, 

 and shows a strong peg-like process upon the inner aspect of its pos- 

 terior end, which is at right angles to the axis of the bone. It fits in 

 the deep conical socket on the side of the quadrate. Beyond its enlarge- 

 ment for the lacrymal the maxillary is a thin, horizontal plate of bone, 

 anchylosed in the usual way at its anterior end. Here it really enters 

 into the apparatus of the cranio facial hinge. A process pointing back- 

 ward and apparently coming from the premaxillary is seen over this 

 horizontal plate of the maxillary on either side. Professor Parker 

 found this condition present also in another species of Sula, and this 

 eminent anatomist also describes a " post-maxillary" for these birds 

 which heightens the zygoma, overlying, as it does, its commencement. 



In this specimen the interorbital septum, which is a thin, smooth 

 plate, shows considerable of a fenestra near its middle, and a few such 

 openings of a very much smaller size pierce its posterior wall. 



The circular optic foramen is entire, is of a size apparently three or 

 four times the caliber of the nerve it passes, and it seems to include the 

 smaller foramen to its outer side. 



The orbital cavity itself in this Gannet is very deep, the eaves of its 

 roof almost overhanging the jugal bar beneath. Its superior periphery 

 is smooth and rounded. All in front of the rhinal chamber is filled in 

 by the spongy mass formed by the united maxillo-palatines. The hinder 

 portions of these bones are, however, still distinct, and they have all 

 the appearance of these elements as they are found in birds which 

 possess them as concavo-convex plates facing outward. 



The rostrum of the sphenoid is a hollow subcvlindrical tube, united 

 above with the interorbital septum. As we proceed anteriorly it be- 

 comes more flattened from side to side, and gradually rises upward. 

 At a point about half way between the palatines and cranio-facial hinge 

 it terminates in a process directed forward ; above this is the sharpened 

 ethmoidal margin, nearly perpendicular to the long axis of the skull. 

 Osseous wings to the ethmoid never develop in Sula, not even rudi- 

 mentary traces of them being seen at their customary sites. 



The cranio-facial hinge is exceedingly perfect in its construction, 

 being composed of a thin plate of bone occupying the full width of the 

 skull ; the bones both above and below are separated from each other 

 by a small interval for the entire length of the transverse line con- 

 stituting the hinge. . Mtl4M 

 Proc. K M. 88 19 ^AyUiyttf- 



