| OCR Text |
Show 160 DR. P. CHALMERS MITCHELL ON THE [May 16, at their insertions. Any well-marked deviation from this condition may be regarded as derivative. I have shown that in the more specialised Columbida? the posterior division of the muscle tends to disappear (4); in the Kingfishers the anterior division similarly is in progressive diminution (5); in most of the Gruiform birds the anterior division is less strongly marked, whilst the posterior division tends to increase greatly in size and strength, whilst in the Crane and Bustard it is the posterior division which disappears (7). In the Limicoline birds generally the anterior division remains in the primitive condition, whilst the posterior tends to enlarge as it does in the Rails, the enlargement being specially a backward and downward extension of the origin. On the other hand, in the Woodcock, as an exception, there is a disappearance of the posterior division. Latissimus dorsi metapatagialis.-This muscle is probably present in all these birds, but it is very slightly developed and apt to be removed in the process of skinning. Rhomboideus superjicialis et profundus.-Of these two muscles, the superficial is phylogenetically older. In all these birds it is the thinner of the two muscles, but is longer, being longest in CEdicnemus and Chionis, whilst it shows a general tendency to die away posteriorly. In Chionis it is nearly divided into a proximal and distal portion by a thin central area, a secondary cleavage which is well marked in the deep muscle of the eutaxic Kingfishers. The deep muscle in Hydrophasianus is almost of the same length as the superficial muscle and it is difficult to separate the two. In the others it is well separated by its greater thickness and by the slope of its fibres upwards and forwards from the scapula to the vertebra?. Its origin begins at the extreme posterior end of the scapula and extends forwards under the origin of the superficial muscle, but never reaching so far forwards. In the condition of these muscles, then, the Limicolae are fairly homogeneous; the older superficial muscle is well developed, extending in front of the deep muscle, but, except in Scolopax, leaving a portion of it exposed behind. The deep muscle has made comparatively little progress in forward extension along the line of the scapula, and clavicle. Biceps brachialis.-This muscle displays in CEdicnemus the condition normal in the majority of birds ; it arises by a narrow tendon from the acrocoracoid, and by a broad tendon from the proximal end of the humerus ; the rounded belly runs down the arm and ends in a forked tendon, the thicker fork being inserted to the radius, the thinner to the ulna. No doubt, fleshy origins must have preceded tendinous origins, and there is considerable variation as to the relative size of the two origins and insertions in diflerent birds; but the CEdicnemus condition is a fairly central one, and it is interesting to notice that in this respect CEdicnemus stands apart from other Limicoline birds and might be associated with many other groups. In Hydrophasianus there is a comparatively slight deviation from the normal, consisting in the complete disappearance |
