THE PIGEON 195 



are ventral, the clavicle being anterior to the coracoid. The 

 glenoid cavity, in which the humerus articulates, is situated at 

 the meeting-point of the scapula and the coracoid. 



The scapulae are a pair of elongated, flattened bones, which lie 

 along the spinal column, attached to it and to the ribs by means 

 of muscles. The coracoids are a pair of thick bones, which lie at 

 right angles to the scapulae and extend between them and the 

 anterior end of the breastbone ; they are firmly joined with both 

 the scapulae and the breastbone. This connection is a very im- 

 portant one, inasmuch as the greater part of the viscera lie in the 

 concave dorsal surface of the breastbone. Note above the glenoid 

 cavity the foramen triosseum, an opening formed by the meeting 

 of a process from the scapula and one from the coracoid. The 

 tendon of the lesser pectoral muscle passes through it. 



The clavicles are ankylosed at their ventral ends and form the 

 wishbone. Their dorsal ends articulate with the coracoids ; their 

 ankylosed ventral ends are joined by a ligament with the keel 

 of the breastbone. 



Exercise 36. Draw the pectoral girdle, with the breastbone. 



The skeleton of the wing is made up of three divisions: a 

 proximal, a middle, and a distal division. The proximal division 

 is composed of a single bone, the humerus. The head of this 

 bone is made up of the rounded articular surface, which fits into 

 the glenoid cavity, and of a small anterior and a large posterior 

 tuberosity. The anterior tuberosity is continuous with the prom- 

 inent deltoid ridge, in which is inserted the great pectoral muscle. 

 In the great tuberosity is the pneumatic foramen, an opening into 

 the hollow center of the bone. The distal end of the bone has two 

 articular surfaces : an anterior one for the radius, and a transverse, 

 posterior one for the ulna. 



The middle division is formed by the radius and ulna, of which 

 the latter is somewhat longer and thicker than the former. At 

 the proximal end of the ulna is the short olecranon process, which 

 forms the elbow. Along the posterior border of the ulna is a row 

 of small elevations, which mark the position of the base of the 

 secondary wing quills. 



