30 DESCRIPTION OF THE SKELETON. 



The ster- The Sternum. — The sternum is a massive bone with a heel beneath, 



num. 



by which its inferior surface is divided into two faces. Anteriorly, the bone 

 is pointed, or has a protuberance two inches thick. From this anterior 

 extremity the sternum becomes wider to its anterior third, which is thirteen 

 inches across. Its posterior part is narrowed, and the sides compressed; 

 the anterior pieces are co-ossified. The anterior extremity of the bone is 

 very rough and irregular for the reception of the inferior extremities of 

 the first rib, with which it is partially co-ossified. The posterior extremity 

 of the sternum is supplied. 

 The Ribs. The Ribs. — The ribs are twenty in number ; thirteen true, and seven 



false. The first rib (Plate XXIII. Fig. 1) differs from all the others in 

 form, having more the appearance of a clavicle than of a rib. It is situated 

 in a vertical direction nearly ; the superior extremities, however, of the two 

 ribs being more distant from each other than are the two inferior. They 

 are placed nearly on a line with the anterior edges of the scapula. This 

 rib may be divided into three parts ; a superior, middle, and inferior. The 

 superior, connecting with the vertebral column, has nearly the form of the 

 superior part of the human os femoris, and admits of three divisions, viz. 

 1st, the head, which is four inches thick, and presents a flat articulating 

 surface to correspond with the first dorsal vertebra ; 2d, the neck, in cir- 

 cumference six inches, presenting a prominence on its superior part ; M, the 

 great tuberosity, with an articulating surface on its vertebral extremity, 

 where it comes in contact with the transverse process. The body of the 

 bone is of a rounded form superiorly. The inferior extremity flattened is 

 broad, massive, irregular, and co-ossified with the sternum ; at its narrowest 

 part it is six inches in circumference. 



The length of the first rib is twenty-eight inches, from which the 



