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Show 164 DR. P. CHALMERS MITCHELL ON THE [May 16, complexity in Gulls, so Gulls exhibit the doubling of the bre\ is tendon and the anchor from the longus to Fiirbringers a, which are the conspicuous features of the Limicoline alar complex. The general trend of change in the formation of the alar tendons seems to have been, first, the formation of distinct tendons from a series of scattered fascise and cutaneous slips, and next a reduction of the complex tendons to a more and more simple form. The most ready interpretation of the facts appears to me to be that in the ancestors of the Laridte and Limicolae a complex and specialised alar series of tendons had been elaborated; this condition has been retained by the Gulls and by most of the Limicolous birds, whereas in the Gruiformes and in CEdicnemus it has more or less completely disappeared, leaving traces such as the separation of the distal fan of the brevis into the small divisions which can be recognised as the a, /3, y of Fiirbringer. Deltoicles major et minor.-In all these birds both muscles are present and display little divergence. The minor is extremely small in Chionis, Gallinago, and Hydrophasianus; in the others it is normal. The major is a muscle which in many birds displays a progressive tendency to creep down the humerus. It is shortest in Hydrophasianus, not reaching more than three-eighths of the proximal end of the humerus, and is without the usual scapular anchor. In Gallinago it reaches rather less than halfway down the humerus, in Thinocorus rather more; in the others nearly an exact half, the scapular anchor being well marked in all but Hydrophasianus. Scapuli-humerales anterior et posterior (text-fig. 26, p. 159).- The posterior muscle (S.P.) is present in all these birds and is large and important, converging from an extensive origin occupying the greater part of the scapula to a rounded tendon inserted to the median process of the humerus. The anterior muscle (S.A.) is small and occupies the usual position across the angle between the scapula and the humerus. It is normal in CEdicnemus and Hydrophasianus, very small, merely a few fibres, in Glareola and Thinocorus. In Charadrius it is small but quite distinct, whilst in Himantopus it is represented by a narrow band of fibres. In Chionis, Vanellus, Hhynchcea, Gallinago, and Scolopax it is absent. There seems little doubt but that the normal, or archecentric, condition in Birds is for both divisions of the muscle to be present, whilst the anterior division is frequently absent. The Limicolaj obviously form a group with a marked tendency to the disappearance of this muscle, but there is no special correlation between specialisation in other directions and the degree of reduction of the muscle. Expansor secundariorum.- T\\e specialised division of the anconseus to which Garrod gave the name of " expansor secundariorum " is a muscle in obvious course of disappearance in this group. It is present in a well-marked condition in CEdicnemus (text-fig. 26, S., p. 159) and Hydrophasianus. Its |