PASSERES. 



459 



In the patagium, that is the triangular membrane of the bird's wing expanded 

 between the anterior margins of the humerus and the fore-arm, the tendons of two 

 muscles are to be found. One is that of the tensor patayii lonyiis, which forms the 

 supporting chord of the free margin itself. The second is that of the tensor patayii 

 brevis, which courses parallel with the humerus from the shoulder to the muscles and 

 fascire of the fore-arm. From the comparatively insignificant fleshy belly of this 

 muscle, a single cylindroid tendon runs to the upper margin of the axially running 

 tendon of origin of the extensor metacarpi radialis longus, at a point not far from 

 the tubercle on the humerus, whence this muscle springs. In most of the Passe-res the 

 tensor patagii brevis here becomes attached to the latter muscles without blending 

 with its tendon, and runs from the point of attachment back, independently fixing 

 itself to the base of the same tubercle as the extensor m. r. lone/us, as a consequence 

 of which arrangement two distinct tendons run to that same spot, as may be plainly 

 seen in the accompanying cut (Fig. 228 A.) In a few Passeres of the South American 

 families Pteroptochidse and Conopophagida?, the arrangement is a little obscured since 

 the muscular fibres of the extensor in. r. lonyus almost surround and enclose the ten- 

 dons in question, but upon removing these covering fibres the two tendons are seen 

 arranged exactly as in most other members of the order. The only real exceptions 

 arc the lyre-bird (IHemtra), and the Australian brush-bird Atrichornis rufescens, in 

 Avhich the tensor brevis inserts itself on the tendon of the extensor tnetacarpi, in such 

 a way as to blend with it entirely, only one tendon running to the tubercle at the 

 elbow, an arrangement which is exactly like that of the Ramphastidae, Megalairnidae, 

 Indicatoridae and Picidas of the foregoing order, and illustrated in Fig. 228 B. 



A certain structure of the syrinx is also peculiar to the Passeres, although not 

 common to all of them. Having already in the introduction to this volume promised 

 a fuller account of this feature, we shall try to make this point as intelligible as pos- 

 sible, especially since the syringeal arrangement 

 has been made the chief character by which some 

 systematists primarily subdivide the Passeres. 



The great German anatomist, Johannes Mid- 

 ler, in 1846 announced the discovery that the 

 Passerine birds exhibited two or rather three 

 radically different types of the lower larynx. 

 He found that in the vast assemblage of birds 

 which has usually been called Oscines, Cantores, 

 etc., the intrinsic muscles numbering from 

 two to six pairs are inserted into the extremi- 

 ties of the bronchial semi-rings, an arrangement 

 which Garrod has termed acromyodous, while 

 the rest have these muscles usually only one pair attached to the semi-rings in 

 their middles ; these are called Mesomyodi, or Clamatores. But of the latter some 

 South American forms are peculiar in having the syrinx chiefly formed by the lower 

 end of the trachea, hence Miiller made them a separate group, Trachcophome ; the 

 Mesomyodi with tracheo-bronchial syrinx are often termed Oligomyodi, or Ilaploophona', 

 though the latter name was original Iv intended for a more restricted group. The 



~ ^j ' 



terminology is somewhat intricate, but it is important that one who wishes to study 

 or understand the modern schemes of Passerine classification should master it thoroughly, 

 hence Fig. 229 is given to indicate the difference between the acromyodian and the 



FIG. 2C9. Syrinx (A) of Africfiornis (acromy- 

 Odian) anil' (II) of Hylactes (mesoniyodian); c, 

 extrinsic, ;', intrinsic muscles; x, bronchial 

 semi-rintis ; /, trachea; the muscles are lined 

 longitudinally. 



