188ti. ] PKOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 287 



At different times anatomists have devoted considerable attention to 

 the structure of these birds, and every year, I think, we are becoming 

 more unanimous upon the affinities they hold with other groups. On the 

 present occasion I can contribute but little to this subject, although a 

 good skeleton of Sula bassana — No. 1G643 of the Smithsonian collection, 

 and kindly loaned me by that institution — will permit me to illustrate 

 the osteology of that representative of the Sulidce. Then I will have 

 somethiug to add about the skeleton in the Cormorants and a word or 

 two about the craniology of Pelecamis. 



OSTEOLOGY OF SULA BASSANA. 



Some of the smaller bones in my specimen are missing, such as the 

 major portion of the hyoid arches, a few ribs, and joints of the toes, but 

 in the main it is in excellent condition, and from it no doubt I can pre- 

 sent a very fair review of the skeleton of this type. 



Sula is noted for the high pneumatic condition enjoyed by almost its 

 entire skeleton. We find this property extended throughout the axial 

 portion of it, with the exception of the ribs and free caudal vertebra 1 . 

 The pectoral limb is completely so, but in the pelvic extremity the femur 

 is the only bone that appears to be pneumatic. 



Of the skull. — In form the superior osseous mandible is flat upon its 

 under side with cultrate tomium, while superiorly it is convex from 

 side to side, and tapers from base to apex gradually to a point, being a 

 little decurved near the extremity. Sometimes we find it pierced by a 

 foramen on this upper side, which leads to its hollow interior, but Sula 

 is without nostrils, though their probable position, did they exist, is 

 perhaps indicated by the posterior end of the longitudinal furrow that 

 marks the mandible upon its lateral aspect (Fig. 24). 



An osseous, thoroughly adherent crust overlies the greater part of 

 this superior surface, the only smooth place being a small area in front 

 of the cranio facial hinge. This envelope is very thin ; nevertheless 

 when compared with the smooth portion found above it its thickness 

 is easily appreciated. Its entire surface is marked all over by an ex- 

 quisite anastomosing venation, the ramifications starting, in some in- 

 stances, from minute foramina in its substance. 



A lacrymal is a free bone, articulating with a roughened facet of some 

 extent beneath the antero-external angle of the frontal above, and by a 

 smooth, gliding facet on the upper side of the maxillary, which latter 

 bone is thickened in a perpendicular direction and otherwise enlarged 

 in order to offer it the proper amount of surface. As for tbe bone itself, 

 it is of rather a columnar form, with the exception of its extended ante- 

 rior margin, which is roundly notched and shows ou its inner side the 

 large pneumatic opening leading to its hollow interior. 



In Gannets there exists, projecting horizontally from the outer mar- 

 gin of the frontal bone, on either side, from its " prefrontal process." a 

 few millimetres posterior to the iron to lacrymal suture, a small rounded 



