68 ANATOMY OF VERTEBRATES. 



in the Pelicans, Cormorants, Grebes, Petrels, Frigate-bird, and 

 Tropic-bird ; also in the Gigantic Crane, and Storks in general. 

 In the Humming-birds, where the sternum is so disproportionately 

 developed, the furculum terminates ahnost opposite the commence- 

 ment of the keel, but at some distance before it ; it is of equal 

 length with the coracoid. As the principal use of this elastic 

 bony arch is to oppose the forces which tend to press the humeri 

 toward the mesial plane during the downward stroke of the mng, 

 and restore them to their former position, the piers of the arch 

 are stronger, and the angle of their union is more open, as the 

 powers of flight are enjoyed in greater perfection : of this adjust- 

 ment the Swifts, Goat-suckers, and Diurnal Birds of Prey afford 

 the best examples. In the Eagle the clavicles are arched both 

 forward and outward, much expanded above, with an articular 

 surface for the fore part of the outer prong of the coracoid. The 

 arch becomes narrower, and the bone itself weaker, as flight 

 is feebler or less sustained ; in the GallincB the U- is changed 

 to the V-shape ; and at the point of confluence of the straight 

 and slender piers a process is continued, usually compressed, 

 sometimes styliform ( Crax), becoming almost obsolete in Hemi- 

 jwdius ; in the Lapwing the process is at right angles to the arch. 

 In Tacliypetes the upper ends of the clavicles coalesce with the 

 coracoids ; and the lower confluent ends expand into a triangular 

 plate coalesced with the sternal keel. In the crested Pintado the 

 apex of the furculum is dilated and hollowed into a cup opening 

 forward and receiving a fold of the windpipe.^ 



In Birds the humerus has a smooth shaft, sub-elliptic in trans- 

 verse section, with expanded ends, the proximal^ one being the 

 broadest. Lengthwise the bone is gently sigmoid, the proximal 

 half being convex palmad, the distal half concave, with the plane 

 of the terminal expansions vertical, as the bone extends along the 

 side of the trunk from its scapulo-coracoid articulation backward, 

 in its position of rest. 



The head of the humerus is an elongate, semi-oval convexity 

 Avith the lono; axis transverse from the radial to the ulnar sides 

 (vertical, as naturally articulated), and with the ends continued 



' XLiv. no. 1411, p. 271. 



^ I here avail myself of the terms indicative of aspect and position proposed by 

 Dr. Barclay, in his 'Anatomical Nomenclature.' 



Proximal signifies the upper, distal the lower, end of the bone, as it hangs in Man; 

 anco7ial is the posterior, palmar the anterior, surface, as when the palm of the hand is 

 directed forward ; radial is the outer, ulnar is the inner, side, according to the same 

 position of the human arm and hand. Proximad, palmad, are adverbial inflections, 

 meaning towards the proximal (upper) end, and towards the palmar (anterior) side. 



