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



similar to others of the same function derived from it, which are still broad thin expan- 

 sions of muscular fibres. In other birds this has either completely disappeared, or has 

 developed thoracically new attachments to other muscles or to bone. 



As regards the other muscles of the anterior extremity, the deltoid is always 

 remarkable for its shortness, extending but a very small distance down the arm (vide 

 PI. IV. fig. 7, d.) frequently allowing the anterior belly of the latissimus dorsi (l.d.) 

 to appear superficially below it. Only in Phcebetria fuliginosa (a nestling specimeu) 

 have I found the special tendinous slip of origin from the scapula which is found in 

 so many birds. 



The triceps has a well-marked tendinous attachment to the humerus superficial to 

 the insertion of the latissimus dorsi. Its muscular belly arises from the scapula by fleshy 

 fibres, and is comparatively short, its tendon, on the other hand, being long, and not 

 joining the tendon of the biceps till over the elbow. 



The latissimus dorsi is in two bellies, as in birds usually ; of these the posterior is 

 much the largest, the anterior being comparatively small and narrow. 



Posterior extremity. 



The gluteus primus is nearly always very small, scarcely or not at all covering 

 the biceps cruris (vide PL V. fig. 1). It is larger in the Oceanitidae, especially in 

 Oceanites (t.c, fig. 3, gl. 1) and Garrodia, where it does cover the biceps to some little 

 extent anteriorly. 



The gluteus quintus appears to be absent, or not differentiated off from the 

 posterior fibres of the preceding, in all the Tubinares, except the Diomedeinas, where it 

 can be distinctly defined. 



The ambiens is present and usually well-developed in all the Tubinares, except the 

 genera Fregetta of the Oceanitidae, and Pelecanoides amongst the Procellariidse, in which 

 it is quite absent. 



In Pelagodroma, Oceanites, and Garrodia its fleshy belly is of fair size, but the 

 tendon I have been unable to trace across the knee, it apparently terminating on the 

 cnemial process of the tibia. In the other genera this tendon crosses the knee as usual, 

 passing in front of the patella, when that is ossified, between the great cnemial process of 

 the tibia and the end of the femur, and ends as usual in the leg. 



The femoro-caudal is always present in the form of an usually not broad ribbon, 

 inserted about half way along the femur (PL V. figs. 2-4, f.c). It does not pass through, 

 as it does in some of the Ciconiiform birds, a sort of pulley formed by the posterior angle 

 of the pelvic bones. 



The accessory femoro-caudal (PL V. figs. 2, 3, a. f.c.) is always present and well- 

 developed, except in the genera Bulweria and Pelecanoides (t.c, fig. 4), where it is quite 



