164 DR. p. CHALMERS MITCHELL ON THE [May 16, 



complexity in Gulls, so Gulls exhibit the doubling of the brevis 

 tendon and the anchor from the longus to Fiirbringer's 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 fascite 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 ancestoi-s of the Laridse and Limicol^e 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 (Edicnemus 

 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 n, /3, 7 of Fiirbringer. 



Deltoides major et minor. — In all these birds both muscles are 

 present and display little divergence. The minor is extremely 

 small in Chionis, GaUinago, and Hydroj)hasianus ; 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 Hydro'phasianus, not reaching more than three-eighths of the 

 proximal end of the humerus, and is without the usual scapular 

 anchor. In GaUinago 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 

 Hydrojyhasianus . 



Scajndi'/mmei^ales anterior et j^osterior (text-fig. 26, p. 159). — 

 The jDosterior muscle (S.P.) is present in all these birds and is 

 large and important, converging from an extensive origin 

 occupying the greater pai-t 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 visual position across the 

 angle between the scapula and the humerus. It is normal in 

 Q^dicnemus and Hydrophasianus, very small, merely a few fibi-es, 

 in Glareola and Thinocorus. In Charadrius it is small but quite 

 distinct, whilst in Himantopn,s it is represented by a narrow 

 band of fibres. In Chionis, Vanelhis, Bhynchoia, GaUinago, and 

 /Scolopax it is absent. 



There seems little doubt bvit 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 Limicol^e 

 obviously foi-m a group with a marked tendency to the disap- 

 pearance of this muscle, but there is iio special correlation between 

 specialisation in other directions and the degree of reduction of 

 the muscle. 



Expansor secundariorimi. — The 'specialised division of the 

 anconseus to which Garrod gave the name of "expansor 

 secundariorum " is a muscle in obvious course of disaj)pearance in 

 this group. It is present in a well-marked condition in 

 (Edicnemus (text-fig. 26, S., p. 159) and Hydrophasiamis. Its 



