158 MAMMALIAN ANATOMY 



triangular roughened area extends toward the mesosternum, offering 

 attachment to the cartilage of the first rib. The lateral border of the 

 manubrium then turns sharply and inclines toward the middle line, 

 and ends by meeting the caudal border. 



The mesosternum is of almost uniform width and thickness. It 

 usually presents on the ventral (anterior) surface a transverse line 

 opposite each costal union, indicating its original separation into four 

 pieces. The lateral border exhibits a half-facet at each end and four 

 intermediate entire facets for the ends of the costal cartilages. The 

 facets for the fifth, sixth, and seventh cartilages are closer together 

 than are the cephalic four. Between the facets the lateral border is 

 distinctly emarginate, forming intercostal notches. 



The xiphisternum is a small, variable piece, usually notched or 

 bifid at the caudal end, and placed in a plane dorsal to the plane of 

 the rest of the sternum. It exhibits at the cephalic end of each lateral 

 border an obscure half-facet for part of the sternal end of the cartilage 

 of the seventh rib. 



HUMAN THORAX. 



The human thorax (Figs. 6, 104) is relatively shorter and wider 

 than the cat's thorax, and its dorso-ventral diameter is relatively 

 smaller. The greater curvature of the ribs renders its walls more 

 regularly arched, and causes the vertebral column to encroach to a 

 greater degree upon the dorsal part of its cavity. The ribs have also 

 a more marked inclination toward the pelvis, which, with their greater 

 width, reduces the width of the intercostal spaces. The inlet of the 

 thorax is reniform, with its transverse diameter twice as long as its 

 dorso-ventral. 



