PIGEON. 31 



COMMON CHARACTERS OF THE RIBS. 



A middle rib should be taken in order to study the typical 

 ■character of the ribs. Each rib presents for examination two 

 extremities, a superior or vertebral, and an inferior or sternal, and 

 an intervening portion — the shaft. The superior or vertebral end 

 shews a head, neck, and tuberosity. The head articulates with 

 the process before described on the body of the dorsal vertebrae. 

 The tubercle presents an oval surface, for anticulation with the 

 ■extremity of the transverse process. The neck is the portion 

 included between the head and the tubercle. 



The shaft is thin and flat. About its middle, from the posterior 

 margin, a process is given off, which curves upwards and back- 

 wards, and overlaps the succeeding rib: this is the uncinate process. 



The first and last have no uncinate process. Each rib 

 articulates infer iorly with a straight rod-like bone — the costal rib 

 — which is to be considered as an ossified costal cartilage. The 

 first two ribs have no sternal ribs, while the last sternal rib does 

 not articulate with the sternum directly, but is blended with the 

 preceding costal rib. 



The thoracic cavity is completed below by the large expanded 

 sternum, which developes from five centres of ossification. This 

 bone is placed in the middle line, and extends over the abdominal 

 cavity reaching to the pelvis behind. 



The upper surface of the body of sternum is deeply concave and 

 boat-shaped, while at its anterior margin is a convex tranverse 

 grove on either side, for the reception of the sternal articulation 

 of the coracoids: these grooves meet in the middle fine. The 

 costal border is thickened, and divided by transverse articula ridges 

 for the sternal ribs into hollows, which shew pneumatic foramina. 



On the inferior surface of the sternum is a largely developed 

 descending vertical process — the keel. This affords additional area 

 for the origin of the great pectoral muscles which move the wing. 



This osseous creast is convex along its inferior margin, being 

 of greatest vertical diameter in front, gradually lessening to its 

 posterior border. Its most anterior extremity is concave. 



Along the lateral margins of the body are two processes on 

 either side, placed behind the articulations for the sternal ribs — 

 these afford attachment for fascia, which strengthens the floor of 

 the abdominal cavity behind. 



SCAPULAR ARCH 



Consists of the scapula, the clavicle, and the coracoid, on each side. 

 The scapula is a- long, thin, recurved sabre-shaped bone, being 

 thickest at the front, where it approaches the shoulder joint, at 

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