592 OSTEOLOGY OF LAEIDiE. 



groups, Lari and Sterna ; the former comprising Lcstris and Larus ; the Ijitter, Sterna 

 and Ehynckops. Yet, once more, some recent ornithologists have judged that the 

 Jaegers, Gnlls, Terns, and Skimmers each represent a distinct family. Not to mention 

 other classifications of the group, I am iu favor of the first of these modes of subdi- 

 vision. The value of the characters which separate the Laridw from the FrocellariidcB 

 is the same as of those distinguishing other families of Natatores; the line dividing 

 them is trenchant ; and there are no aberrant forms in either.* 



The four subfamilies of the Laridw, while equally well defined, have yet genera 

 upon their coniines which serve to connect them with each other and with other 

 families. Witness the cered biU of Stercorarivs, by which it approaches the Procellariida, 

 but is in nearly every other particular essentially a Gull. Such subgenera as Xema and 

 Creagrua among Larincn change the Larine very gradually to the Sternine form, meet- 

 ing, on the confines of the latter subfamily, such a subgenus as the thick-billed, short- 

 tailed Gelochelidon, to render the transition still less abrupt. And the Ehyiichopince are 

 in every respect true Terns, exce^it in the feature of the unique bill. Examination of 

 the internal as well as the external characters of the four subfamilies (Lestridince, La- 

 rina, Siernin(B, and Bhynchopinw) demonstrates that the first and second and the third 

 and fourth are more nearly related to each other than are the second and third. 



With these brief remarks upon the family in question, I proceed to give a detailed 

 account of Its osteology, the skeletons of the four subfamilies being so similar that I 

 have thought it best to consider them collectively, indicating subfamily discrepancies. 

 The splanchnology of the four differs more extensively ; and I have, therefore, consid- 

 ered the viscera of each under the head of its typical species, except as regards those 

 of the Rhynchopirue, which are so similar to those of the Siernbice that I have omitted 

 them altogether. Other minor points of splanchnic details I have presented when 

 considering the more marked species. I had hoped to have given the myology of the 

 family in detail, but want of time and space forbade. 



OSTEOLOGY. 



Craxia. — The skull of the Ehynchopwce differs in so many and so essential respects 

 from that of the other three subfamilies that it has been deemed advisable to describe 

 it sejjarately. The others may Ije most conveniently described together, in connection 

 with the general osteology of the family, any differences of importance being, as is the 

 case with the rest of the skeleton, pointed out. The skulls selected for description are 

 those of Stei'coraritis pomatorkinns, Laints argentatm, and Sterna hirundo, each being con- 

 sidered as typical of its respective subfamily. In this case I use ordinary anatomical 

 terms, for the most part, without reference to any theory of the composition of the skull. 



The general shape of the skull, as in by far the majority of Aves, is that of an elon- 

 gated pyramid with a tetragonal base. Its greatest length is from the occipital pro- 

 tuberance to the apes of the intermaxillary bone ; its greatest depth from the middle 

 of the parietal anchylosis directly downward to the base of the sphenoid ; its greatest 

 width is from one tympano-zygomatic articulation to the other. This pyramid is 

 shortest and broadest iu Stercorarius, narrowest and most elongated in Sterna. 



On the base of the pyramid the superior curved line of the occiput is well marked ; 

 the perpendicular spine less developed ; the surrounding surfaces of boue are only 

 slightly depressed. Tlieforamen magnum is rather large, and of a nearly circular shape. 

 The occipital condyle is small, but stands out as a prominent very convex hemisphere. 

 There are well developed " mastoid" processes. 



The temporal fossa on either side of the superior aspect of the skull is not very 

 deep, indicating a rather small aggregate of temporal and masseter muscles. It is 

 incompletely divisible into two portions — a posterior, which stretches toward the 

 median line just anterior to the occipital ridge ; and an anterior, which constitutes the 

 depression just behind the posterior orbital processes. This division is most marked 

 in Larus, and is hardly apparent in Stercorarius. In neither of the subfamilies do these 

 fossae approach very near to the median line, and there is thus left a much more ex- 

 tensive, elevated, smooth portion on the vertex than exists in other natatorial genera, 

 as Puffimis, Colynibvs, &c., where the broad and deep fossse are only separated bj a 

 narrow ridge. The vertex is marked by a smooth longitudinal depression denoting 

 the bi-parietal suture. The anterior and posterior orbital processes are well developed, 

 the former esx^ecially, which project directly outward and backward, with no down- 

 ward obliquity. The posterior ones incline at a considerable angle downward. The out- 

 line of the orbital ridge included between them differs in each subfamily, owing to the 

 difference in the shape and position of the " nasal " glands. In Larus these glands are 

 almost wholly contained, except jnst at their anterior termination, in very deep, well- 

 marked fossse, so that they project but little over the real bony margin of the orbit. 

 In Stn-na, on the contrary, the concavity of the outline of the orbital ridges is very 

 great, the skull being exceedingly narrow at that point, and therefore the glands 



' Audubon has, indeed, included the Jaegers among the Procellariidce, on the strength 

 of their unentire bill. The error of such a procedure, however, needs no comment. 



