156 MAMMALIAN ANATOMY 



ventral curvature, and that its ventral end has a marked caudal 

 inclination, turning upward when the rib is laid with its cephalic 

 edge upon the table. The shaft is twisted to a greater degree round 

 its long axis, the caudal-medial surface assuming at the sternal end a 

 more caudal direction. 



The head of the human rib is flatter and bevelled at the expense 

 of the dorsal surface. The caudal (inferior) part of its articular 

 surface is much larger than the cephalic (superior) part. 



The neck is long, slender, and prismatic. The tubercle is relatively 

 smaller; as in the cat's rib, its articular surface faces in a caudal, dorsal, 

 and medial (inferior, inner, and posterior) direction. It is separated 

 laterally by an oblique line from a prominence for the insertion of a 

 costo-transverse ligament. 



The shaft is prismatic in its vertebral part, but becomes flattened 

 and expanded in its sternal part. 



The cephalic-lateral (external) surface appears as the continuation 

 of the dorsal surface of the neck. It is very slightly convex in its 

 cephalo-caudal width ; of course, strongly convex in its dorso-ventral 

 length ; more decidedly convex in its vertebral part. It is marked at 

 the angle by a short oblique line. 



The vertebral part of the caudal-medial (internal) surface is 

 divided into two areas by an oblique line running from the ventral 

 border of the neck to the dorsal-caudal border. The dorsal triangular 

 area is a groove for the intercostal vessels. The ventral area forms 

 part of the inner wall of the thorax, and is slightly convex from the 

 ventral-cephalic to the dorsal-caudal border, and, of course, strongly 

 concave from the vertebral to the sternal end. 



The costal cartilage is relatively shorter, stouter, and less curved. 



CHARACTERS OF THE REMAINING HUMAN RIBS. 



The ribs increase in length from the first to the seventh or eighth, 

 and then successively decrease to the last. The intermediate ribs are 

 broader and flatter, and their terminal sternal surface is linear. 



The First Rib is the most curved, the strongest and the shortest, 

 and has the longest neck. It lies for its whole extent nearly in 

 one plane. Its head has a single articular facet. The tubercle is 

 high ; the shaft has no angle. Its cephalic surface is crossed by two 

 shallow grooves for the subclavian vessels. Between the grooves on 



