390 ON THE PETRELS COLLECTED DURING 



developed in the Tubinares, in the form of a broad, thin band, more or 

 less parallel with the coracoid, occupying the superior half of the broad 

 space between that bone and the furcula, its fibres arising chiefly from 

 the strong membrane between these bones, sometimes with additions 

 from the anterior margin of the coracoid, or from the body of the sternum 

 close to the middle line. 



Tensor patagii brevis and longus. These muscles have always a common, 

 rather thin and flat fleshy belly, arising from the extreme upper end of 

 the clavicle, and receiving, in addition, special small slips from the sur- 

 face of the great pectoral. From this fleshy belly spring two tendons, 

 of which one always forms the marginal patagial tendon, and must 

 therefore be considered as the tensor patagii lonyus. Both the tendons 

 are connected, close to their origin, by fibrous slips to the humeral crest, 

 from which indeed they might be said to arise, receiving then the main 

 muscular belly. The connection of the marginal tendon with the 

 humerus is always provided with a small tract of strong elastic tissue 

 (vide PL XVIII. fig. 3, t.p.V.), and another such tract of longer extent 

 is found on its course opposite the bend of the elbow (PL XIX. fig. 4 

 and PL XVIII. fig. 3). 



In other respects the development and distribution of these tendons 

 differs much in different groups of genera, and their arrangement will 

 therefore be here considered seriatim. 



It is in the Oceanitidse that the disposition of the tendon of the tensor 



patagii brevis (t.p.b.) is simplest, it here, in all the four genera, passing 



Zool. Chall. straight downwards as a thin band, parallel to the humerus, to be lost on 



Exp. vol. iv. ^Q asc i a C0 vering the outer side of the forearm. In Procettaria, Cymo- 



chorea, Halocyptena, and Pelecano'ides (vide PL XIX. fig. 2) 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 (PL XIX. 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 banJcsi the wrist- 

 ward slip goes mainly to the deep belly of the extensor, sending off a 

 thin band to the more superficial one. Erom 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. 



