THE VOYAGE OF THE ' CHALLENGER.' 395 



birds this lias 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. XVIII. fig. 3, d.), frequently allowing the anterior 

 belly of the latissimus dorsi (l.d.) to appear superficially below it. Only 

 in Phoebetria fuliginosa (a nestling specimen) 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 glutens primus is nearly always very small, scarcely or not at all 

 covering the biceps cruris (vide PI. XX. 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 yluteus quintus appears to be absent, or not differentiated off from 

 the posterior fibres of the preceding, in all the Tubinares, except the 

 Diomedeinae, where it can be distinctly defined. 



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

 except the genera Fregetta of the Oceanitidse, and Pelecano'ides 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 a usually not 

 broad ribbon, inserted about halfway along the femur (PI. XX. 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 XX. figs. 2,3, a. f.c.) is always present 

 and well-developed, except in the genera Bulweria and Pelecano'ides (i.e., 

 fig. 4), where it is quite absent. It is fairly broad and ribbon-shaped, Zool. ChaU. 

 overlapping the semi-membranosus in the Oceanitidffi at its origin, Ex P- voLir. 

 and inserted into the femur together with the femora-caudal. In the. ptxl< P- 31 - 

 genera Fregetta, Puffinus, and Majaqueus it is decidedlv small. 



