MTOLOGT OF OPISTHOCOMUS CEISTATUS. 355 



prominent, and preserves the diameter of its ridge very uniformly throughout its length ; 

 the pectorals are, also, of an equal thickness throughout the whole of their sternal 

 attachments; and the crop disports itself awkwardly enough upon their superficial 

 aspect and the receding furcular angle, more especially when moderately distended. 

 The Oj}isthocomus illustrates a perfect crop and calyx-like receptacle ; but the Pheasant 

 only the former, its nidus being referred to a rugged and uncomfortable habitat. 



Probably the most remarkable feature in the sternum is the prominent tubercle 

 (PI. LXIII. tb) in which the distal extremity of the keel terminates. It appears as an 

 ovoid surface, somewhat flattened, and projecting to a corresponding level with the 

 superficial surface of the pectorals, the fibres of which it separates at this particular 

 spot. It is only covered by the integument, which is condensed upon it and closely 

 connected with it. In the bird undivested of its plumage it can be readily seen — the 

 skin over the tubercle being destitute of feathers. The keel in front and behind the 

 tubercle bevels off in an arcuate manner, the posterior border being inconsiderable in 

 length. The pectorals adapt themselves to a nicety to the alternating width of the 

 keel, throughout its extent. Section of the pectoral muscle shows its gradually in- 

 creasing thickness from the furcula to the double angular distal bends of the muscle. 

 Its proximal attachments are similar to those of the generality of birds, viz. to the 

 whole length of the furculum, keel of the sternum, to the distal margin of the lateral 

 half of the sternum, and also to its lateral shelving plate (external xiphoid process) 

 external to the attachment of the second pectoral. The under or sternal surface of the 

 great pectoral is channelled for the accommodation of the 2nd pectoral and its minor 

 associate. The muscle undergoes considerable condensation at its distal extremity, 

 immediately prior to its insertion into the delto-pectoral ridge of the humerus. At the 

 latter point it has some tendinous fibres mingled, but sparingly, with the muscular. 



From the middle of the superficial aspect of the insertional fibres, a few detach 

 themselves as a small wedge-shaped muscle, about ^ an inch long (PI. LXIV.) ; this 

 speedily terminates in a slender tendon, and receives the anterior portion of the differen- 

 tiated deltoid muscle. The conjoined tendon traverses thebrachium as far as the lower 

 end of the humerus, where it divides into two tendons : the anterior one is inserted into 

 the tendon of origin of the extensor carpi radialis longior ; and the posterior, smaller 

 than the preceding, crosses the outer aspect of the extensor muscles, continues its course 

 along the bases of the wing-feathers as a fascial expansion, and is finally lost upon the 

 dorsal aspect of the carpus. This tendon gives slips of attachment to all the cubital 

 feathers except the last three or four. 



There is another small muscle (PL LXIV. fig. 3) which arises from the fascia covering 

 the biceps, immediately below the lower border of the great pectoral muscle. Its 

 muscular belly is three quarters of an inch long, fusiform in shape, and ends in a slender 

 tendon, which traverses the cubit as far as the base of the 1st metacarpal. These 

 muscles constitute the extensor plicae alaris of Professor Owen \ 



' Prof. Owen (Anat. & Phys. of Vert. vol. ii.) deeoribes this estensor as consisting of " two portions, of which 



■ 3b2 



