20 POFLTKY DISEASES 



last cervical vertebra and the first dorsal segment. The last 

 rib articulates witli the under side of the ilium at its ante- 

 rior alar portion. Tliis rib is situated similar to the true ribs, 

 but instead of articulating directly with the sternum the sec- 

 ond portion lies against the second portion of the rib just 

 anterior to it. The ribs are provided with two articular 

 facets on the dorsal portion, and these articulate with simi- 

 lar facets on the dorsal vertebrae. The true ribs are called 

 sternal ribs, and each succeeding sternal rib is longer than 

 the one preceding it. Nearer and nearer these ribs assume a 

 horizontal position. The proximal end of the sternal rib 

 articulates with the distal end of the vertebral rib. Th.e 

 sternal end is provided with two small ridges. 



From the posterior border of the second, third, fourth and 

 fifth vertebral ribs and near their middles are flat uncinate 

 l)ony processes projecting upward and forward overlying the 

 succeeding rib, giving greater surface for muscular attach- 

 ments and greater stability to the thorax. The vertebral por- 

 tion of the rib (32) articulates inferiorly with the sternal 

 portion (41) joining it to the sternum or breastbone, with 

 which it articulates. The two portions of the rib are joined 

 by a diarthrodial articulation. The uncinate process of the 

 rib (31), is flat and projects backward onto the succeeding 

 rib, giving added stability to the thorax. These processes 

 are absent from the first and last ribs. 



The sternum or breastbone is a large four-sided plate of 

 bone, the posterior portion of which overlaps the ribs on the 

 outer side. On the inferior portion of the sternum there is 

 a leaf-like ridge called the crista sterna or breast ridge 

 (or keel). This bony expansion gives a greater surface for 

 the attachment of muscles. 



The sides are provided Avith an external and an internal 

 process forming an internal and an external notch. These 

 notches are bridged over by a broad ligament, to which the 

 muscles are attached. In the poor flyers, as the fowls, these 

 notches are large. The sternal end posteriorly is called tlie 

 zyphoid process. Anteriorly it is provided Avith lateral ex- 

 ternal processes, the costal processes. In the center of the 

 anterior part is the episternal process. 



LIMBS 



The OS scapulare (24) is elongated, narrow and presents 

 smooth surfaces. Anteriorly it forms a portion of the gle- 

 noid cavity and is united to the fork of the coracoid bv menus 

 of fibro-cartilage. 



The OS clavicula (33) terminates l»eh>\v in the hypocU'idcnm 



