THE VOYAGE OF THE 'CHALLENGER.' 393 



The presence of these peculiar wing-ossicles is thus confined to the 

 Diomedeinae, and to the genera Majaqueus, Puffinus, Bulweria, and (Estre- 

 lata (in which last there is only one), and, according to Reinhardt (5. c., 

 p. 133), Adamastor, of the Procellariinae. In the genus Freyata there is 

 a similar small bony nodule developed at the point where, as in the 

 Petrels, the inner part of the tensor patayii lonyus tendon meets the 

 tendon of the superficial belly of the extensor metacarpi, and from it 

 radiate out tendinous fibres to the patagial margin. 1 have observed 

 similar ossicles, developed at points of intermittent straining, in several 

 other birds, as Larus aryentatus and ylaucus, Fratercula arctica, and 

 Merops. 



These bones must be considered to be of the nature of sesamoids, 

 which, as is well known, are often developed in the tendons of muscles 

 at the points of greatest strain. Their occurrence therefore in different 

 groups of birds is by no means a proof of any genetic connection be- 

 tween such. 



Biceps This muscle, in all Tubinares, is remarkable for its excessive 

 reduction, the muscular bellies being small and short, and the tendon 

 of insertion excessively narrow and thin (vide PI. XIX. figs. 1, 2, and 

 PI. XVII. fig. 1,6). 



It is best developed perhaps in the Diomedeinae, where as usual it 

 arises by two heads, a coracoid and humeral (vide PL XVII. fig. 3,o., Ji.\ 

 both, however, being largely tendinous, and soon uniting. From the 

 coracoid head is given off a very narrow slip, chiefly tendinous, with a 

 few fleshy fibres only, which runs down in the patagium, and joins the 

 margin of the patagium formed by the tensor patayii lonyus close to the 

 elbow (PL XVII. fig. 3, and PL XIX. fig. 4, &..). 



In the Oceanitidas the biceps muscle is very slender. It has the two 

 usual heads of origin, the tendons of these being often closelv uni'ed 

 together by fibrous tissue, and ending in a small short, common belly. 

 This apparently gives off no " biceps-slip " at all *. 



In nearly all the other Procellariidae, including Pelecanoides, the biceps Zool. Chall. 

 becomes modified in a peculiarly interesting way. The coracoid head Exp.vol. iv. 

 alone forms the muscle proper, whilst the humeral head, becoming 

 detached from the coracoid head, goes entirely to the tensor patayii lonyus 

 tendon, which it joins as a short, cylindrical tendon close to the shoulder 

 (PL XVII. fig. 1, h.). It is, therefore, functionally a " biceps-slip," though 

 it differs from the ordinary " biceps-slip " found in so many birds t, in 



* The dissection of these parts in this group of birds is attended with considerable 

 difficulty, partly owing to the smallness of the various parts involved, partly to the 

 great accumulations of fat round the tissues, making the true nature of these very 

 difficult to determine in spirit-specimens. It would be very des-'rable to dissect out 

 these parts in fresh specimens. 



t Of. Garrod, Coll. Papers, p. 324. 



