26 THE VOYAGE OF H.M.S. CHALLENGER. 
as a thin band, parallel to the humerus, to be lost on the fascia covering the outer side 
of the forearm. In Procellaria, Cymochorea, Halocyptena and Pelecanoides (vide 
Pl. IV. fig. 6) it is nearly equally simple, but as it passes over the superficial belly 
of the extensor metacarpi radialis longior (e.m.) it gives off to it a small tendinous slip, 
which les on the wristward side of the main tendon. 
In the genus Prion (PL. IV. fig. 1) the condition of things is slightly more complicated. 
The superficial belly of the extensor m.r.l., (e.m.) is quite tendinous throughout, with 
no fleshy fibres at all; where the tensor patagii brevis (t.p.b.) crosses it the two 
tendons are firmly fused together, and there is also a well-developed wristward slip sent 
off from the main tendon of the tensor patagii to meet the extensor tendon 
beyond this junction. The main tensor tendon where it crosses the extensor 
muscle is quite free from it in most cases, though occasionally a few fleshy fibres may 
arise from its anterior margin to join the deeper belly of the extensor m.r.l., (e.m). 
Tn a specimen of Prion banksi the wristward slip goes mainly to the deep belly of the 
extensor, sending off a thin band to the more superficial one. From the point of 
junction of the wristward slip with the extensor tendon, a thin fan-shaped tendinous 
fascia is sometimes sent off to the patagium generally. 
In Gstrelata brevirostris (Pl. IV. fig. 2) the condition of things is similar, but the 
patagial fan is more strongly developed, and the tendinous superficial part of the 
extensor metacarpi is split, proximad of the tensor patagii, one part arising superficially 
to, the other (e.m.*) deep of, the prominent supracondylar humeral process. 
In the genus Gstrelata proper—as represented by Gistrelata lessoni (Pl. IV. fig. 4), 
(strelata mollis, and an undetermined species—the arrangement differs considerably from 
that observed in Gistrelata brevirostris.. The tensor patagii brevis tendon, which 
is more or less fused above with the marginal tensor patagi longus tendon (¢.p./.), 
develops at its junction with the superfigial tendon of origin of the extensor (e.m.)— 
this being, as in Cstrelata brevirostris, double—a small, elongated ossicle (a) from 
which arise not only tendinous fibres—some of which form a patagial fan, whilst others 
but also a number of muscular fibres which form 
the belly of the superficial part of the extensor. The tensor patagit brevis continues 
on in the usual manner to the ulnar fascia. No bony nodule, it is to be observed, is 
join the marginal tendon directly: 
* The condition above described as obtaining in @strelata brevirostris was exactly the same in all the specimens, 
eight in number, dissected. Unfortunately all these were young birds, though the largest must nearly have attained 
its mature plumage, and was probably able to fly. In other young birds in the group that I have examined the 
disposition of these elbow tendons is always exactly the same as in the adults, and even when these last develop 
ossicles here, such ossicles can be found, in a cartilaginous condition, in quite young birds. I have no reason there- 
fore to suppose that the differences described here as existing between Wstrelata brevirostris and the other species of that 
genus are due to any difference in age. 
[P.S.—Since the above was written, Mr. R. Ridgway has been kind enough to examine, at my suggestion, the skins 
of this species in the Smithsonian Institution, and finds, as he informs me, no difference in the development of the 
ossicle between this and the other species of the genus. The question, therefore, requires further material to eluci- 
date it.] 
