OSTEOLOGY 41 



brae which are distinct in the body of the newly hatched chick, but 

 which become fused soon after hatching. With these vertebral 

 segments there are fused the last dorsal and first coccygeal vertebral 

 segments. This fusion is so complete that the segments are in- 

 dicated only by the intervertebral foramina on the sides through 

 which the spinal nerves pass, and by transverse markings on the 

 inferior surface of the bodies. 



The lumbo-sacral vertebrae, called the sacrum, and the ilia are 

 fused. The dorsal spines of the vertebral segments are indicated 

 only in the anterior portion where they are fused, forming a plate. 

 There are no prominent ventral spines. 



The Coccygeal Vertebrae (Fig. 4, No. 27). Location. The 

 coccygeal or caudal vertebrae, or vertebrae coccygeae, constitute the 

 bones of the tail. 



Description. There are seven coccygeal vertebrae. The last 

 segment, shaped like a plough share and therefore called thepygo- 

 style, is the largest and is supposed to have been formed by the 

 fusion of several original distinct segments. It supports the coc- 

 cygeal oil gland and the row of rudder feathers, or rectrices, which 

 are arranged fan-wise. 



All of the coccygeal vertebrae except the first are freely movable, 

 thus allowing the tail to be used as a rudder during flight. The 

 lateral spines are long and well developed, and the superior 

 spines are bifurcated, thus giving increased surface for muscular 

 attachment. The first coccygeal segment is fused with the last 

 lumbo-sacral vertebra. 



THE THORAX 



The dorsal vertebrae superiorly, the ribs laterally, and the sternum, 

 or breast-bone inferiorly, form the skeleton of a large cavity called 

 the thorax. The dorsal vertebrae have been described. 



The Ribs (Fig. 4, No. 32; Fig. 10, A and B). Location. The 

 ribs form the lateral bony wall of the thorax, articulating superiorly 

 with the dorsal vertebrae. 



Description. The ribs are arranged in order of length, the ultimate 

 rib being the longest. From anterior to posterior, they approach 

 more nearly a horizontal position. The ribs are divided into the 

 true and the false. The true ribs articulate with the sternum. The 

 false ribs do not touch the sternum; they are floating. The true 

 ribs are composed of two parts, a vertebral, or dorsal, and a sternal, 



