THE RIBS. 157 



begins to turn broad, and continues so to its anterior end, which 

 is hollow and spongy, for the reception of, and firm coalition 

 with, the cartilage that runs thence to be inserted into the^ter- 

 num, or to be joined with some other cartilage. In adults, the 

 cavity at this end of the ribs is generally smooth. 



The substance of the ribs is spongy, cellular, and only covered 

 with a very thin external lamellated surface, which increases in 

 thickness and strength as it approaches the vertebrae. 



To the fore end of each rib a long, broad, and strong cartilage 

 is fixed, which reaches the sternum, or is joined to the cartilage 

 of the next rib. This course, however, is not in a straight line 

 with the rib : for the cartilages generally make a considerable 

 flexure, the concave part of which is upwards; therefore, at 

 their insertion into the sternum, they make an obtuse angle 

 above, and an acute one below. These cartilages are of such a 

 length as never to allow the ribs to come to a right angle with 

 the spine ; but they keep them situated so obliquely as to make 

 the angle very considerably obtuse above, till a force exceeding 

 the elasticity of the cartilage is applied. These cartilages, as 

 all others, are firmer and harder internally than they are on 

 their external surface ; and, sometimes, in old people, all their 

 middle substance becomes bony, while a thin cartilaginous 

 lamella appears externally. The ossification, however, begins 

 frequently at the external surface. The greatest alternate 

 motions of the cartilages being made at their great curvature, 

 that part remains frequently cartilaginous after all the rest is 

 ossified. 



The ribs then are articulated at each end, and that behind 

 is doubly joined to the vertebrae ; for the head is received into 

 the cavities of two bodies of the vertebra?, and a larger tubercle 

 is received into the depression in the transverse process of the 

 lower vertebrae. When we examine the double articulation, we 

 must immediately see, that no other motion can here be allowed 

 than upwards and downwards. Since the transverse process 

 hinders the ribs to be thrusted back, the resistance of the sternum 

 on the other side prevents the ribs coming forward ; and each 

 of the two joints, with the other parts attached, oppose its 

 14 



