190 NATURAL UlSTOllY OF BIRDS. 



portion of the rook, and on tlie Little Binl." The nest is usually built of grass or 

 sea-weeds, which the birds tear off with their sharp beaks, aud a single egg of a chalky 

 whileiicss, but usually stained and soiled, is deposited, from which is hatched a naked 

 slaty-blue chick, soon to be covered with snow-white down. The adults arc white, 

 head and neck above washed with buff, bill bluish-gray, feet slate-color with light 

 green stri]H'S, indicating the course of tlie tendons; eye yelUtw. The immature birds 

 are dusky, speckled all over with white sjiots. 



A few allied species inhabit the tropical se:is of the eastern hemisjihcre, and a 

 grou]) of smaller, more or less dusky-colored gannets are entirely inter-lropical. In 

 general habits tluy differ but little from the typical species, and altogether there are 

 at present hardly ten different forms. The fact that fossil Sulida' have been found in 

 France in miocene fresh-water deposits indicates, however, that this family formerly 

 •was wider distributed and richer in forms. A miocene iSida is also known from North 

 Carolina. 



The two following families are |)robably more closely related inter se than they are 

 to any of the foregoing. The following are a few characters which the cormorants 

 and the darters have in oonunon, and in which ihey differ from pelicans and gannets: 

 They have twenty vertebne in the neck, against seventeen to eighteen ; the ninth 

 vertebra is the first one pressed back prea.\ially, and not the eighth; the twentieth to 

 twenty-fourth vertebrae in the cormorants, and the twenty-second to twenty-fifth 

 vertebraj in the darters, are opisthoca?lous, while none liave that character in the 

 pelicans and gannets; the latter ])ossess a s])iiial feallier-sjiace, which the former have 

 not, but these have an occipital style unknown in the others. This occipital style is a 

 triangular, elongated bone, articulating with the tubercle on the middle of the upper 

 edge of the occipital bone. The object of this process is to afford surface for the 

 insertion of "the sujierticial temporal muscles meeting behind the skull along the 

 median raphe, which becomes ossified to form the above-mentioned style in the adult 

 bird." A myological feature, which is not shared by the two foresioin^ families, is 

 that the biceps muscle of the arm sends a fleshy slip to the middle of the pat.agial 

 tendon of the tensor jxitagii longns. Finally may be mentioned the very backward 

 position of the hind limbs, wliich force the cormorants and darters to carry their body 

 more erect than the other members of the order. 



The cormorants, I'iiai,ackocoracid-«, are readily distinguished from other Stegan- 

 opods by the combination of a strongly hookol bill, in shajie and structure like that 

 of the frigate-bird, — long neck, short wings, aiul rather long, rounded tail. The 

 head is often crested, and head and neck frequently adorned with thin filamentous 

 jjlumes, which are assumed towards the jiairing season, and disajipear after the 

 breeding. 



We reg.-nd this family as the central one of the order, hence the negative nature 

 of the characters including the anatomical features, the status of which is best found 

 by consulting the diagnoses of the other families. Here shall only be mentioned the 

 peculiarity of the ambiens muscle in passing through tlie substance of the large tri- 

 angular ]>alella in a liony canal. 



The cormorants form a very homogeneous group of nearly forty existing forms, 

 and even the tertiary cormorants seem to be very closely allied to the typical species 

 of the jiresent day, indicating that the group has assumed its jieculiarities at quite a 

 distant ])eriod. 



On account of this uniformity, nobody who ever saw a cormorant will be in 



