TROPIC-BIRDS. 181 



part of the carina, superficial to the pectoralis secundus, and from the symphysial 

 half of the outer border of the furcula. The superficial layer is inserted by a broad 

 linear attachment to the pectoral ridge of the humerus, whilst the deeper layer ends 

 in a rounded tendon." According to Garrod, this arrangement is exactly alike in 

 Plotus, Phaethon, Pelecanus, /Sula, and also in Phalacrocorax, though not so easily 

 recognized in the latter. The birds of other orders which show a similar condition, 

 are the American vultures, the storks, and the petrels. 



Professor Huxley, in enumerating the characters of the ' Dysporomorphae,' as he 

 styled this order, indicates that the phalanges of the anterior toes decrease in length 

 from the basal to the penultimate. A re-examination of the gi-oup has convinced me 

 that this is not correct. It will be seen from the figure, further on, of the bones of 

 the foot of Fregata, that the ratio of the phalanges is quite different, the basal ones 

 of the second and third toes being shorter than the next ones. A similar ratio is 

 also found in the gannets, especially the smaller species, and likewise in the darters. 



In common with the frigate-birds, the PHAETHONTOIDE J5 have a compara- 

 tively lai'ge head, mounted on a short and thick neck, consisting of fewer and nor- 

 mally articulated vertebrae. The wings are long and pointed, the tail cuneate, with 

 the two middle feathers extremely lengthened. The feet are rather small, but the 

 webs are ample ; they are totipalmate, like all the members of the order, that is, 

 even the first toe is connected with the next one by a membrane ; and in this particu- 

 lar group it is short, and turned nearly forwards. Another peculiarity of the hind 

 toe is that it articulates with the metatarsus considerably above the level of the other 

 toes, herein differing from the other members of the order. The claw of the third 

 toe is not pectinated. In having an undivided sheath, without any groove or detached 

 pieces, the bill resembles that of a tern, but the edges are serrated. Like the 

 terns, the tropic-birds have pervious nostrils, therein differing considerably from 

 the other members of the order, in some of which the external openings of the nares 

 are absolutely closed in the adult birds ; but in contradistinction to the terns and gulls, 

 the tropic-birds are strongly holorhinal. Additional osteological characters will be 

 mentioned under the descriptions of the other groups, though we may remark here 

 that the hind border of the breast-bone has two notches, and, consequently, two lateral 

 processes on each side, somewhat similar to the condition in the gulls. 



The myological peculiarities are described thus by Gai'rod: "Phaethon possesses 

 the femoro-caudal (small), the semitendinosus (strong), and the accessory semitendi- 

 nosus ; the ambiens, the accessory femoro-caudal, and the postacetabular portion of the 

 tensor fasciae are absent. In this bird the biceps cruris is inserted into the fibula-head 

 directly, without passing through a loop." 



Pterylographically there is only little difference between the present super-family 

 and the Pelecanoidea3, but the structure of the feathers is different, they being more 

 elastic and more curved, rather resembling, according to Nitzsch, those of the geese. 

 The skin is pneumatic, similar to that of the gannets, and each oil-gland has three 

 openings. 



The tropic-birds an appropriate name for these intertropical birds are also 

 called ' boatswains,' for the same reason as the jaegers, namely the extremely elongated 

 middle tail-feathers. In their general aspect, the white color of the body, and the 

 red or yellow bills, size, etc., they closely imitate the gulls or terns ; and many travel- 

 ers have described their habits as similar to the latter, but the resemblance seems to 

 be very slight and very superficial. The tropic-birds are very oceanic, and are often 



