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Show 8 PROF. W. LILLJEBORG ON THE CLASS OF BIRDS. [Jan. 9, the branches of trees*. The hinder extremities or the legs exhibit, in conformity with this, three different forms. This induces us to divide the class of birds into three primary groups or subclasses :- 1, Natatores; 2, Cursores ; 3, Insessores. Those belonging to the third group generally move more with the assistance of their wings than the others, except some forms of the Natatores, and show generally a higher development of the bird-type. This group also furnishes the greatest variety of forms. The Natatores include about 550 species, the Cursores 900, and the Insessores 6900 (Bonaparte). Nitzsch has, in the treatise referred to, divided the class of birds into three groups : Aves aerese, Aves terrestres, and Aves aquaticse, which in a reverse order correspond with the three groups here arranged ; but he differs from us in including the Columbine birds among the Terrestres, and the Grallatorial birds among the Aquaticse, and in considering the Struthionine birds a distinct group from the other three. There is, as far as experience yet extends, a very remarkable correspondence between the nature of the upper wing-coverts and of the carotides communes, which adds to the importance of both these characters, which have generally been but little observed. All those birds that have the large upper wing-coverts of the first row on the cubitus so short that they do not reach beyond the middle of the cubital quills, have only one carotis communis, viz. the sinistra. Those birds in which the above-mentioned wing-coverts form several rows and extend beyond the middle of the cubital quills, have, on the contrary, generally two carotides communes, viz. one dextra and one sinistra. The only exceptions to this rule are Cypselus, Trochilus, Merops, one or a few species of Psittacus, Rhea, Phosnicopterus, Podiceps, and Pelecanus, which, although belonging to the latter category in regard to the wing-coverts, yet have only one carotis communis. This is the dextra in Phcenicopterus. W e do not, therefore, hesitate to consider these two characters to be among the most important in judging of the affinity of the birds ; and they show with certainty that the birds of prey have not their place at the beginning or at the end of the system. The Strisores, one of the twelve orders in which we have arranged the class of birds, includes several birds that we formerly considered should belong to the Passeres, from their near correspondence in form with the latter. But as they deviate from them in regard to the upper wing-coverts and the claw of the hind toe, and sometimes even in regard to the carotides communes, we are of opinion that they should be regarded as belonging to a different order. They have been separated from the Passeres by Sundevallf and by Nitzsch; and the former has arranged them under the order Coccyges, which' according to him, also includes the Zygodactyli and Columbce'. Ihey are, however, distinct from the Zygodactyli in the nature of their feet, and cannot be arranged under this order without depriving I The second mode appears an intermediate link between the first and third t Xongl. Vetensk. Acad. Handl. 1843, pp. 375 & 376. |
