THE BIBS, THE STEENUM. AND THE THOKAX 



157 



the medial border is an elevation for the attachment of the scalenus 

 anticus muscle. The caudal surface has no groove for the intercostal 

 vessels. 



The Second Rib is flat, but is longer and narrower than the first. 

 Its shaft is more regularly arched, and has a faint intercostal groove. 



The Tenth Rib is long and curved, is marked by a deep intercostal 

 groove, and presents but a single articular facet on its head. 



The Eleventh Rib has no tubercle, only traces of an angle and a 

 groove, and a single facet on the head. 



The Twelfth Rib has neither tubercle nor groove, and a small, 

 single, capitular facet. 



The cartilages of the first three ribs are directed ventrally, those 

 of the remaining ribs ventrally and toward the head. The cartilage 

 of the eighth rib is the longest. 



HUMAN STERNUM. 



The sternum in man (Fig. 104) is a narrow and flat plate which 

 late in life forms a single piece of bone, but before complete coalescence 

 of its parts consists of an hexagonal 

 cephalic piece, the manubrium or pre- FIG. 104. 



sternum ; a much longer body, or meso- 

 sternum ; and a short terminal ensiform 

 process, or xiphisternum. Its length is 

 about three times as great as its maxi- 

 mum width across the manubrium. It 

 is gently arched ventrally along its 

 cephalo-caudal axis. On each side it 

 affords direct attachment to seven costal 

 cartilages, whereof one is attached to 

 the manubrium, one between the manu- 

 brium and the body, four to the body, 

 and one between the body and the ensi- 

 form process. 



The cephalic border of the manu- 

 brium presents the median interclavic- 

 ular notch, on each side of which is an 



oval, saddle-shaped area, the clavicular notch for union with the 

 sternal end of the clavicle. From the caudal end of this notch a 



FRONT VIEW OF THE THORAX. 



1, 2, 3, the three pieces of the sternum ; 4, 5, 

 the thoracic vertebrae; 6, the first rib; 7, its 

 head; 8, neck; 9, tubercle; 10, the seventh 

 rib; 11, costal cartilages: 12, the floating ribs; 

 13, groove for the intercostal blood-vessels. 



