SHUFELDT : OSTEOLOGY OF THE STKGANOPODES 205 



The lacrymal is a free bone articulating by its upper portion with the free border 

 formed by the frontal and nasal bones, while its descending limb is bulbous at its 

 lower extremity, and fails to reach quite the maxillary below it. The pars plana 

 is nearly aborted, there being merely a small bridge of bone left, that arches over 

 the anterior end of the nasal nerve as it enters the rhinal chamber. This nerve 

 passes in an open groove, but is again shielded by an osseous span, just as it enters 

 the orbit. The "foramen rotundum" is large and is distinct from a still more exten- 

 sive vacuity which is seen above it on the anterior wall of the cranial casket. No 

 foramina exist in the interorbital septum proper. Occasionally a small distinct 

 nerve foramen is seen to the outer side of the opening for the exit of the optic 

 nerve. The anterior border of the mesethmoid is both concaved and sharpened 

 (PL XXIX., Fig. 45). 



The zygomatic bar is quite straight, being transversely compressed at its quadrato- 

 jugal end, to become twisted upon itself in the jugal part, and so vertically flattened 

 for the remainder of its extent or in the maxillary moiety. The extreme anterior 

 end fuses in between the premaxillary and nasal. At the hinder extremity we find 

 the usual little peg articulating in the pitlet on the outstanding process of the 

 quadrate (PI. XXIX., Figs. 45 and 48). 



As has already been remarked above, one of these last-named bones bears a 

 very close resemblance to the quadrate, in an albatross. The orbital process 

 of the os quadratum in Fregata is antero-posteriorly compressed just as it is 

 in Diomedea, and its free extremity is expanded and finished off in the same 

 manner. 



We notice a slight difference, however, in the form of the internal articular 

 facet of the mandibular end of the bone. It is more compressed from before, back- 

 wards in Fregata, and the articular surface presents but one common convexity, 

 whereas in Diomedea this facet is impressed by a deep, oblique valley, the axis of 

 which is parallel to the pterygoid of the same side. 



As in the Albatross, a pterygoid bone is a straight, stout element, with some- 

 what enlarged anterior end, and a markedly expanded posterior one ; in the last 

 character being much more enlarged than it is in Diomedea. Both birds have their 

 pterygoids pneumatic, and when articulated in situ, they touch each other in the 

 middle line, beneath the sphenoidal rostrum. 



In Fregata the basitemporal region is small and of a triangular outline ; the 

 eustachian passages are very open canals, and their anterior beginnings are separated 

 by quite an interval the base of the sphenoid standing distinctly between them 

 (PI. XXIX., Fig. 48). 



