102 PRACTICAL ANATOMY. 



a lower larger, separated by a well-defined horizontal 

 ridge. The neck, flattened antero-posteriorly, is rough 

 for the attachment of ligaments and muscles. It is 

 about one inch long, and lies in front and above the 

 transverse process of the vertebra below. At the pos- 

 terior inferior part of the neck, at the junction of the 

 neck with the shaft, is the tuberosity, a rough elevation 

 of bone, well marked in the upper ribs. It presents an 

 articular surface for articulation with the extremity of 

 the transverse process of the vertebra below. The shaft 

 is a flat, curved portion of the bone, which arches for- 

 ward to the costal cartilage. It presents for examination 

 an external and internal surface, superior and inferior 

 borders, an angle and sternal extremity. The external 

 surface, convex from above downward, curved from 

 behind forward, presents, external to the tuberosity, the 

 angle, at which the shaft makes an abrupt bend forward 

 and downward. The angle becomes gradually farther 

 removed from the tuberosity in passing from the second 

 to the tenth rib. It is an oblique ridge, which affords 

 attachment to the dorsal aponeurosis. The inner surface 

 of the shaft is convex from above downward, and pre- 

 sents some small foramina for the nutrient vessels to the 

 bone. The superior border is smooth and rounded ; the 

 inferior border is sharp and grooved along the inner sur- 

 face for the passage of a branch of the intercostal artery 

 and nerve. The sternal extremity is oval, concave, cov- 

 ered with cartilage, and articulates with the convex head 

 of the costal cartilage. The ribs, with some exceptions 

 (eleventh and twelfth), are developed by three centres, 

 one for the head, one for the tuberosity, and one for the 

 shaft. The first, second, tenth, eleventh, and twelfth ribs 

 are peculiar. The first rib differs in that its vertebral 

 end, or head, has but one articular surface ; it has no 



