42 ANATOMY OF THE DOMESTIC FOWL 



or ventral. The vertebral part, or extremitas vertehralis, is provided 

 with an articular head, or caput casta; a neck, or coUum costa; 

 and an articular tubercle, or tuberculum casta. The head and 

 tubercle articulate with the dorsal vertebra. Below the head of 

 each rib is a pneumatic foramen. 



The distal extremity of the dorsal section of the rib articulates 

 with the proximal end of the sternal section by a diarthrodial 

 articulation. 



The articulations of the true ribs with the sternum is diarthrodial 

 and each articulate by two small ridges with a double sternal facet. 

 The first, the second, and the seventh ribs are floating, or false 

 ribs. The first rib articulates with the quadrate part of the last 

 cervical vertebra and also with the first dorsal vertebra. The 

 seventh, the last rib, articulates with the under side of the anterior 

 alar part of the ilium. This rib is situated similarly to the true ribs; 

 but, instead of articulating directly with the sternum, the lower end 

 lies against the sternal segment of the rib just anterior to it. 



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

 the fifth ribs, and near the middle of the dorsal segment, are flat, 

 uncinate, bony processes which project upward and backward, over- 

 lying in each case, the succeeding rib and giving greater surface for 

 muscular attachments and greater stability to the thorax. 



The Sternum (Fig. 4, No. 40; Fig. 10, No. A,g). Lacation. — The 

 sternum, or breast-bone forms the inferior portion, or floor of the 

 thoracic cavity. 



Descriptian. — The sternum is a quadrilateral, curved plate with 

 processes projecting from each angle and from the middle of the 

 anterior and posterior borders. The posterior medial projection, 

 or metasternum, is the longest, and has a tall, plate-like ridge — 

 ■the sternal crest, crista sterni — running along its ventral surface. 

 The crest serves the important function of increasing the bony area 

 for the attachment of the powerful muscles which move the wings. 

 The anterior medial projection, or rostrum, is short, and pierced 

 at its root by an opening from which extend two elongated, saddle- 

 shaped depressions into which the end of the coracoid bones are 

 received. 



The plate-like process of bone, the posterior lateral process, which 

 projects from the caudal angles of the sternum soon divides into two 

 parts. The shorter of these, the oblique process, broadens toward its 

 free end and covers the sternal segments of the last two ribs. The 



