50 THE VOYAGE OF H.M.S. CHALLENGER. 
metacarpt radialis longior muscle. This is least developed in Pelecanoides and 
Thalasseca. 
The pectoral crest, on its inferior aspect, presents an elongated surface for the attach- 
ment of the great pectoral, coextensive with the lower moiety of its border. This surface 
develops a roughness at each extremity, particularly below, where the main part of the 
more superficial layer of the muscle is attached by its strong tendon. The double nature 
of the pectoral muscle is indicated by a distinct muscular ridge dividing the general area 
of insertion into two. 
In the Oceanitide the humerus is conspicuously a stouter and shorter bone, with its 
shaft evidently curved, instead of beimg almost straight. The epicondylar process 
projects much less forwards, and is continued down by an elevated ridge to the surface of 
the condyle itself. 
In the Albatrosses the humerus is distinctly concave forwards, with its shaft consider- 
ably compressed throughout. The pectoral crest is sharply pointed, the bicipital surface 
very prominent and convex, the internal trochanter less developed, and the infra-capitular 
fossa very shallow, with its apex occupied by a large pneumatic foramen, and the 
brachialis impression long and very shallow. 
In Pelecanoides, as might have been expected from its diving habits, the humerus is 
somewhat modified from the ordinary Procellarian type. The shaft of the bone is 
comparatively short and much compressed, especially below, where it has sharp anterior 
(external) and posterior (internal) margins. The pectoral crest is little developed. ‘The 
internal condyle descends considerably lower than the external one, and the capitellar 
surface is well-developed and compressed. Behind it and the external condylar trochlea 
is a strongly-marked deep pit, into which fits, like a peg, a sharp conical process 
developed at the proximal end of the ulna. The epicondylar process is very short, and 
the depression for the brachialis anticus very shallow. 
The radius is a slender, straight and cylindrical bone, with its distal end depressed 
and grooved superiorly. 
The wna is much stouter, with its posterior edge sharply keeled, with only slight 
impressions for the secondary remiges. The olecranon process is short and bluntly 
triangular. In Pelecanoides the radius and ulna are considerably compressed from before 
backwards. The ulna is stout, and develops at its proximal end a slightly curved 
triangular process, directed upwards, which, as already described, fits into a corresponding 
socket on the humerus, and so firmly unites the bones together. 
The manus is very long. The second and third metacarpals are nearly parallel 
and straight, the third metacarpal being much more slender than its fellows. The pollex 
has but one phalanx, which is strong and long, about equalling one-half of the second 
metacarpal. The two phalanges of the index are well-developed, the basal one, which 
does not articulate with the third digit, being much dilated posteriorly. 
