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 fasciz 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 Laride and Limicole 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 Wdicenemas 
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. 
Deltoides 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; m the others 
it is normal. The major isa 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 Zhinocorus 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(S8.P.) is present in all these birds and is 
large and important, converging from an extensive origin 
occupying the greater part of the scapula toa rounded tendon 
inserted to the median process of the humerus. The anterior 
muscle (8.A.) is small and occupies the usual position across the 
angle between the scapula and the humerus. It is normal in 
Edienemus 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, Rhynchea, Gallinago, and 
Scolopax it is absent. 
There seems little doubt but that the normal, or archecentrie, 
condition in Birds is for both divisions of the muscle to be present, 
whilst the anterior division is frequently absent. The Limicole 
obviously form a group with a marked tendency to the disap- 
pearance of this muscle, but there is no special correlation between 
specialisation in other directions and the degree au reduction of 
the muscle. 
Expansor secundariorum.—The specialised bined of the 
anconeus 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 
Gdicnemus (text-fig. 26, 8., p. 159) and Hydrophasianus. Its 
