470 



PRACTICAL ANATOMY. 



2. Tlic base, formed by the musculo-aponeurotic diaphragm. 



3. An anterior wall, formed by the sternum and costal chondra or cartilages. 



4. A posterior wall, formed by the thoracic vertebra; and the ribs to the angle. 



5. Lateral walls, formed by the rib from angle to costo-chondral joint. 

 There are twelve ribs on each side twenty-four ribs in the typical human 



thorax. Each rib articulates with the vertebral column posteriorly ; the seven 

 upper ribs articulate in front with the sternum, being called, on this account, true 

 ribs. Of the five lower ribs, three have their ventral end secured in this manner : 

 the eighth is attached to the cartilage of the seventh, the ninth to the cartilage 

 of the eighth, the tenth to the cartilage of the ninth rib. The ventral ends of the 

 eleventh and twelfth ribs are free, /. c., unattached, and are called floating. 

 A typical rib, the seventh, should be studied systematically as to : 



1. A head, which has two facets and a horizontal crest. 



2. A neck, which intervenes between the head and the 'tubercle. 



3. Tubercle, which consists of an articular and a non-articular part. 



4. An angle, the place where the rib bends in two directions. 



5. The Shaft. This has two surfaces and two borders. 



6. The outer surface is for the attachment of muscles. 



Spinous process of seventh 

 cervical vertebra 



Capsular ligament of first 

 costo-central joint 



Capaular ligament of the first coeto-trans- 

 verse joint 



FIG. 345. THK C'ATSULAR LIGAMKNTS OF THE COSTO-VERTEBRAI. JOINTS. 



7. The inner surface, has the subcostal groove for nerve and vessels. 



8. The superior border, which is thick and rounded. 



9. An inferior border, which is sharp and thin. 



10. The subcostal groove lodges the intercostal vessels and nerves. 



Give the rule for the articular part of the head of a rib. 



There are two facets, separated by a horizontal ridge. The ridge is for the 

 attachment of the interosseous ligament between the rib and the intercentral 

 disc of fibro-cartilage. 



/ Vliat practical observation can be made regarding the lower articular facet on 

 the head of a rib ? 



This one is the larger of the two, as a rule, and articulates with the thoracic 

 vertebra which corresponds to it in number from above down. The upper is 

 the smaller, and articulates with the vertebra next above. 



Are there any exceptions to the rule of costal facets on the heads of ribs ? 



Yes. As exceptions, may be mentioned the first, tenth, eleventh, and twelfth 

 ribs, each of which has one facet only on its head, as a rule. 



Does the rid articulate witli the vertebral column at any otfier point ? If so, 

 explain fully the rule. 



