SEC. IV ANATOMY OF BIRDS 217 



demi-facet, which represents the share it takes in forming the 

 glenoid (Gr. yk-qvr], glens, a shallow pit ; Fig. 59, gl) cavihj, which is 

 the socket of the humerus. This articular expansion is the glenoid 

 process of the coracoid : the clavicular process is that by which the 

 bone unites with the clavicle. The relation between the heads of 

 the three bones (each uniting with the other two) is such that a 

 pulley-hole is formed, through which plays the tendon of the pec- 

 toral muscle which elevates the wing. The coracoid is a very 

 constant and characteristic bone of birds. 



The Scapula (Lat. scapula, the shoulder-blade; Figs. 56, 59, s) 

 merits in birds its name of " blade-bone," being usually a long, thin, 

 narrow, sabre-like bone, which rests upon the ribs — usually not far 

 from parallel with the spinal column, and near it'; but in Ratitos 

 otherwise. It seldom gains much width, and is quite thin and flat 

 in most of its length ; but it has a thickened head or handle, 

 expanding outwards into a glenoid process which unites with that of 

 the coracoid to complete the glenoid cavity, and dilated inward to 

 form an acromial (Gr. aKpibfiiov, akromion, point of the shoulder) 

 process for articulation with the clavicle (as it does in man), when 

 that bone exists. The other end is usually sharp-pointed, but may 

 be obtuse, or even clubbed, as in a woodpecker. The scapula is 

 broadest and most plate-like in the penguins, in which birds all the 

 bones of the flipper-like wing are singularly flattened. In Apteryx 

 it reaches in length over only a couple of ribs ; in most birds, 

 over most of the thorax ; and in some its point overreaches the 

 pelvis. 



The Clavieles, or Fureulum (Lat. clavicula, a little key : 

 fwculum, a little fork; Figs. 56, 59, cl), or the clavicular arch, are 

 the pail' of bones which when united together form the object well 

 known as the "merrythought" or "wish-bone," corresponding to 

 the human collar-bones. They lie in front of the breast, across the 

 middle line of the body, like a V or U ; the upper ends uniting as 

 a rule both with scapula and coracoid. For this purpose, in most 

 birds, the ends, are expanded more or less ; such expansion is 

 called the epiclidivm (Gr. Ittij epi, upon ; KkeiSlov, hleidion, the 

 collar-bone) ; in Passerine birds it is said to ossify separately, and 

 is considered by Parker to represent the procoracoid of reptiles. At 

 the point of union below, the bones often develop a process (well 

 shown in the domestic fowl) called the hypoclidium (Gr. viro, hypo, 

 under; Fig. 59, lie), supposed to represent the interclavicle of 

 reptiles. The clavicles are, as a rule, present, perfect, ankylosed 

 together, articulated at the shoulder ; in a few birds ankylosed 

 there; in several, there and with the keel of the sternum; in 

 Opisthocomus there and with the manubrium of the sternum. In 

 various birds, chiefly Picarian and Psittacine, they are defective. 



