150 COUES ON THE OSTEOLOGY 



The disposition of the fibro-cartilage above noticed, by which the glenoid cavit}^ is aug- 

 mented in depth, is strictly homologous with the raised border of cartilage which surrounds 

 the same cavity in man, and which subserves the same purpose. The same plan, accord- 

 ing to Owen, 1 exists throughout the lower orders of birds, the Rasores, Natatores, and Grah 

 Mores ; while in the more highly organized birds, the Raptores and Inscssores, there is 

 found a distinct bone, the " os scapulare" or "os humero-scapulare" which subserves the 

 same purpose. 



Humerus. This bone is moderately long for the size of the bird, but quite stout and 

 strong, and especially notable for the extensive development of the crests and processes 

 near its proximal extremity. It measures between seven and a quarter and seven and a 

 half inches in extreme length. The shaft is centrally very nearly circular on a section ; 

 towards both extremities of the bone it soon becomes flattened in a plane about half-way 

 between the vertical and horizontal, — at the distal extremity to form the two condyles ; 

 at the proximal, to expand into the well-marked superior and inferior crests. The superior 

 crest is very high and long, extending from the articular head to beyond the middle of the 

 bone before it is obliterated; but it is only conspicuously elevated for about one and a half 

 inches of its length, for the greater part of which extent it affords attachment to the broad 

 tendon of the great pectoral. Mesial to this crest, on the shaft of the bone, about an inch 

 from the head, is the small tubercle for the attachment of the conjoined tendinous slips 

 from the latissimus dorsi and the long extensor cubiti. The inferior crest curves as usual 

 in the opposite direction from the superior. It is much shorter, broader, and thicker than 

 the superior, and is placed obliquely to the shaft of the bone, that is to say, parallel with 

 the inward inflexion of the proximal end of the shaft towards the glenoid cavity. Its under 

 surface presents well marked the ordinary deep fossa ; its superior surface near the articular 

 head of the bone also another fossa, more shallow, however, than the inferior. The proximal 

 extremities of both of these crests are marked with several tubercles and facets for the 

 insertion of various muscles, the majority of all the muscles which act upon the humerus 

 being inserted into one or the other of them. 



Between the proximal extremities of these crests is situate the articular head of the bone. 

 It is of an oval shape, exceedingly convex in its transverse, less so in its longitudinal axis. 

 Its face is placed obliquely with reference to the shaft of the bone, from the fact of that 

 part of the bone which supports it curving inwards to meet the glenoid cavity. Its long 

 axis, which is placed directly between the extremities of the superior and inferior crests, is 

 not quite vertical, but inclines obliquely outwards and upwards. The nature of its con- 

 nection with, and movements in, the glenoid cavity, have already been adverted to. 



The distal extremity of the bone presents well marked the great peculiarity which 

 characterizes the elbow-joint of the class Aves; namely, the hemispherical tubercle for the 

 ulnar articulation, and the elongated oblique tubercle, extending somewhat along the shaft 

 of the bone, over which the radius moves. The necessity for the very peculiar shape of 

 these articulating facets arises from the obliquity of their plane in relation to the plane of 

 the circle which the ulna and radius describe in the unfolding of the wing. The articular 

 facets do not project directly outwards, but obliquely downwards and outwards, so that, in 

 the folded wing, the distal extremities of the ulna and radius are below the level of and 

 external to the proximal extremity of the humerus. Now, in extension of the forearm, by 

 the peculiar motion which the radius has over the elongated oblique tubercle with which 



l In Todd's Cyclopaedia of Anatomy and Physiology, Article Aves. 



