. The structure and life of birds . Fig. 75.—Sternum of Ostrich. Rhea, the Emeu and the Cassowary. Thus some tenspecies out of the eleven thousand are disposed of. I must now mention a few of the points that arcmost useful for deciding to which order one of theCannate belongs. Very important are the followingquestions: the presence or absence of the first toe,and the arrangement of the four toes when all are 384 THE STRUCTURE AND LIFE OF BIRDS chap. present ; the relation of the branched tendon thatflexes the toes to that which flexes the hallux (seep. 167) ; the presence or absence of the amb
. The structure and life of birds . Fig. 75.—Sternum of Ostrich. Rhea, the Emeu and the Cassowary. Thus some tenspecies out of the eleven thousand are disposed of. I must now mention a few of the points that arcmost useful for deciding to which order one of theCannate belongs. Very important are the followingquestions: the presence or absence of the first toe,and the arrangement of the four toes when all are 384 THE STRUCTURE AND LIFE OF BIRDS chap. present ; the relation of the branched tendon thatflexes the toes to that which flexes the hallux (seep. 167) ; the presence or absence of the ambiens muscle(see p. 169) which passes from the pelvis to the toes ;the distribution of the feathers on the neck and back—whether there is a clearly defined tract of featherson the neck with bare spaces or apteria on either side,and whether this tract forks, an apterion dividing it. Fig. 76.—(a)—after Nitzsch—Snipe, spinal feather tract divided ; (b) Black-bird, tract undivided. into two arms, when it reaches the back ; whetherthere is an oil gland at the root of the tail, and whetherthis, if present, is bare or tufted with feathers ; whetherthe young are helpless when born, whether they areborn naked or covered with down, and, if naked,whether they pass through a down-stage before theirfeathers grow ; whether the hinder part of the ster-num is entire or has notches or apertures ; what is thenumber of feathers in the tail. xv CLASSIFICATION 385 The few species, the Ratita^, which we haveseparated off from the rest, are held to have inthem less of what constitutes a bird than any will now go to the other end of the scale, themost highly specialized of the Carinatae. These arethe Passeriformes or sparrowlike birds, the largestorder of all. Of the 367 birds which Mr. HowardSaunders counts as British, 125 belong to this leaves 242 for the ot
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