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 Proeellaria, Cymochorea, Halocyptena and Pelecanoides (vide 

 PI. 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 lies on the wristward side of the main tendon. 



In the genus Prion (PI. 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). 

 In 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 CEstrelata brevirostris (PI. 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 CEstrelata proper — as represented by CEstrelata lessoni (PI. IV. fig. 4), 

 CEstrelata mollis, and an undetermined species — -the arrangement differs considerably from 

 that observed in CEstrelata brevirostris. 1 The tensor patagii brevis tendon, which 

 is more or less fused above with the marginal tensor patagii longus tendon (t.p.l.), 

 develops at its junction with the superficial tendon of origin of the extensor (e.m.) — 

 this being, as in CEstrelata brevirostris, double — a small, elongated ossicle (a) from 

 which arise not only tendinous fibres — some of which form a patagial fan, whilst others 

 join the marginal tendon directly — but also a number of muscular fibres which form 

 the belly of the superficial part of the extensor. The tensor patagii brevis continues 

 on in the usual manner to the ulnar fascia. No bony nodule, it is to be observed, is 



1 The condition above described as obtaining in CEstrelata 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 CEstrelata brevirostris and the other species of that 

 genus are due to any difference in age. 



[KS. — 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.] 



