THE HUMAN BODY. 



to various regions of the Body. The sacral foramina, anterior 

 and posterior, are the representatives of these apertures, but 

 modified in arrangement, on account of the fusion of the 

 arches and bodies of the vertebrae between which they lie. 



Sternum. The sternum or breast-bone (Fig. 27 and d, 

 Fig. 16) is wider from side to side than dorso-ventrally. It 

 consists in the adult of three pieces, and seen from the ven- 

 tral side has somewhat the form of a dagger. The piece M 

 nearest the head is called the handle or manubrium, and pre- 

 sents anteriorly a notch, Id, on each side, with which the 

 collar-bone articulates (u, Fig. 16); farther back are two 

 other notches, Id and Jc2, to which the sternal ends of the 

 first and second ribs are attached. The middle piece, C, of 

 the sternum is called the body; it completes the notch for 

 the second rib and has on its sides others, 

 Ic 3-7, for the third, fourth, fifth, sixth, 

 and seventh ribs. The last piece of the 

 sternum, P 9 is the ensiform or xiphoid 

 process; it is composed of cartilage, and 

 has no ribs attached to it. 



The Ribs. (Fig. 28). There are twelve 

 pairs of ribs, each being a slender curved 

 bone attached dorsally to the body and 

 transverse process of a vertebra in the 

 manner already mentioned, and continued 

 ventrally by a costal cartilage. In the 

 case of the anterior seven pairs, the costal 

 cartilages are attached directly to the sides 

 of the breast-bone; the next three carti- 

 lages are each attached to the cartilage of 

 the preceding rib, while the cartilages of 

 the eleventh and twelfth ribs are quite 



FIG. 27. The sternum ,, .-, TI j 



seen on its ventral aspect, unattached ventrally, so these are called 



the free or floating ribs. The convexity 

 of each curved rib is turned outwards so 

 rib-cartiiages. " " as io ^ rouil( j nes8 to the sides of the 



chest and increase its cavity, and each slopes downwards from 

 its vertebral attachment, so that its sternal end is consider- 

 ably lower than its dorsal. 



The Skull. (Fig. 29) consists of twenty-two bones in the 

 adult, of which eight, forming the cranium, are arranged so 

 as to inclose the brain-case and protect the auditory organ, 



