50 THE VOYAGE OF H.M.S. CHALLENGER. 



metacarpi rad talis longior muscle. This is least developed in Pelecanoldes and 

 Thalassceca. 



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 Oceanitidas the humerus is conspicuously a stouter and shorter bone, with its 

 shaft evidently curved, instead of being almost straight. The epieondylar 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 Pelecancndes, 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 epieondylar 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 ulna 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 Pdecanoldes 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. 



