594 OSTEOLOGY OF LAEID^. 



aspect of the skull. Along the median line the stout, broad edge of the conjoined 

 bases of the occipital and sphenoid, and further on of the sphenoid and ethmoid, ex- 

 tend about as far as opposite the fronto-maxillary suture ; there they terminate in a 

 small acutely-pointed process. 



The palate bones are rather widely separated anteriorly ; but posteriorly, by an in- 

 crease of their width, they are brougbt into close apposition, and nearly meet together 

 over the ridge of the sphenoid. They are exceedingly thin and delicate ; their external 

 borders straight ; their posterior extremity more or less abruptly rounded or truncated, 

 bearing at its internal angle the usual small projecting process for the pterygoid artic- 

 ulation. They are completely anchylosed with the superior maxillary, so that all traces 

 of their union are lost. They vary slightly in shape and in comparative length, in the 

 different subfamilies, but not to any notable degree. The inferior surface in all of them 

 is more or less concave in a transverse direction, from the curving downward of the 

 margins. 



The internal or mesial edge of the palate bone has joined to it, along its anterior 

 moiety, the vomer. This is small and light, projecting forward from between the di- 

 vergence of the palatals, on the median line, to divide the nasal passages into two. 

 This bone is bifid for about its third, when the two sides become firmly united, present- 

 ing inferiorly a sharp, narrow edge ; superiorly a broader margin, which is deeply 

 grooved for nearly its whole length, to enable it to ride over the ridge of the ethmoid. 

 The bone is thin and delicate throughout, terminating anteriorly in an extremely at- 

 tenuated apex. 



The malar bones, or "zygomatic arches," are long and slender, having a considerable 

 outward convexity. They are thin and compressed throughout their length, except just 

 where they fuse with the superior maxillary, when they become perpendicularly de- 

 pressed instead of laterally compressed, so that they may yield by their elasticity to an 

 upward motion of the facial bones. 



The malar process of the os pedicellatum is elopgated and well developed, carrying 

 the head of the zygoma far outward and downward. The articulation is of the ordi- 

 nary character. The orbital process of the tympanic bone is moderately long, and 

 compressed and broad, and with a wide, truncated, somewhat nodulated, extremity. 

 The body of the bone is short and thin, being compressed in a lateral direction, but, 

 like the orbital and malar processes, its other processes are all largely developed and 

 quite strong. Its articulation with the os temporale proper is by two very convex, 

 rounded eminences on either side of the articulating head of the bone, separated by a 

 deep notch, which is deprived of a smooth articulating surface. The proper articula- 

 tion of the pterygoid bone is merely a very small prominent convex condyle, which is 

 received into a corresponding cavity in the head of the pterygoid bone. The head of 

 the latter, however, is rather wide, and is in apposition with the edge of the pedicel- 

 latum for a greater extent than is apparent on a slight inspection. In consequence 

 of the development of the malar and pterygoid eminences of the pedicellatum, the ar- 

 ticulating surface for the inferior maxilla is much elongated transversely, and very 

 narrow antero-posteriorly. Its surface, as usual, is irregular. 



The pterygoid bones are of moderate length, nearly straight, their superior borders 

 thin and sharp ; their anterior extremities slightly curved, and with something of a 

 groove to play along the edge of the basilar process of the sphenoid. Their articula- 

 tion with the palate bones is of the ordinary character. 



Lack of basipterygoids may prove a diagnostic feature of Laridm as compared with 

 Procellariidm ; for they are certainly present in many of the Cecomorphw, contrary to 

 the original definition of that group. A late writer has shown that they occur per- 

 haps throughout Procellariidce, and has proposed upon this basis to separate the latter 

 under the name of Xcctriomorpliai. 



The superior maxillary bones are small and inconspicuous. They are so wedged 

 between the intermaxillary, malar, and palatal, that, if we except that process 

 which perhaps belongs to them, which forms the posterior boundary to the nasal aper- 

 ture, they are only apparent internal and superior to the palatal bones, where they 

 form on either side a broad, thin concavo-convex dOation, the concavity of which pre- 

 sents outward and downward. The inferior curled margins of this, their dilation, may 

 be seen on the inferior aspect of the skull, just within and between the palatals, on 

 either side of the vomer, commencing about opposite its extremity. 



The inferior maxillary bone retains at all ages, as usual among Natatores, very evi- 

 dent traces of the original elements of which it was composed. The suture by which 

 the symphyseal elements are united to the supposed conjoined angular and supra-an- 

 gular is specially noticeable, and the splenial element may be distinctly traced on the 

 iusiiie of the ramus of the jaw. This sjplenial element is very short (especially in 

 Siercorarius), and has but little of a forward obliquity. The union of the other pieces 

 of the jaw is complete in adult life. The rami are united at the symphysis for an ex- 

 ceedingly short distance iu Larus and Stercorarius, more extensively in Sterna. The 

 coronoid jjrocess is moderately arched, but the convexity is very gradual, and has no 

 sharp apex. The angle on the lower margin of the jaw, just at the gomphosal suture, 

 is pretty prominent. The outline of the tomial edge of the rami is nearly straight to 



