112 SKELETON. 



The second bone of the sternum is longer and narrower than 

 the first. At its lower part it increases somewhat in breadth, 

 and then terminates by being rounded ofFon either side, so that 

 its margins converge towards each other. The sides of this 

 piece afford complete pits for the third, fourth, fifth, and sixth 

 ribs; the pit for the seventh is common to it and the third bone, 

 as the pit for the second rib is common to it and the first bone. 

 The sixth and seventh pits are in contact, the fifth is very near 

 the sixth, the fourth is about half an inch above the fifth. On 

 viewing the whole side of the -sternum, it will be observed that 

 the distances between the pits decrease, successively, from the 

 first to the last. 



The third bone of the sternum, in the young adult, is fre- 

 quently in a great degree or wholly cartilaginous, hence, the 

 name of xyphoid cartilage (cartilago xyphoides or ensiformis) 

 has been applied to it. It is thin, varies remarkably in its 

 breadth in different individuals, and has the lower extremity 

 sometimes turned forwards and sometimes backwards, but most 

 frequently it is inclined or>ly slightly forwards. The base of 

 this piece presents a narrow oblong surface for articulating with 

 the second bone, at each end of which is the half fossa for the 

 seventh rib. The margins of the ensiform cartilage are thin, 

 and have the transverse muscles of the abdomen inserted into 

 them. Sometimes the lower extremity, instead of being point- 

 ed, is bifurcated. 



The sternum is composed of a spongy texture, enveloped by 

 a thin layer of compact substance. Its strength depends, in a 

 great degree, on its ligamentous covering. 



SECT. IX. OF THE CARTILAGES OF THE RIBS. 



These are placed at the anterior extremities of all the ribs, 

 the seven superior of which they unite to the sternum by the 

 sychondrosis articulation. The length, breadth, and direction 

 of these cartilages are far from being uniform. 



The first costal cartilage is short; the following ones increase 

 in length, successively, to the seventh, inclusively. The carti- 



