114 SKELETON. 



surface, very closely united to the anterior extremity of the cor- 

 responding rib. The other or sternal extremity in the sternal 

 cartilages, offers a smooth articular face, which is angular or 

 convex, according to the shape of the cavity in the sternum with 

 which it has to articulate. The three first ahsternal, and the 

 last sternal cartilage, make, to the lower part of the thorax, a 

 broad and well marked margin, convex in front and concave 

 behind. 



The cartilages of the ribs are, in persons of middle age, white, 

 flexible, and very elastic. They are dissolved very slowly in 

 boiling water; by which they, if young, are reduced to gelatine, 

 otherwise their solubility is very imperfect. They have a 

 structure differing, in some respects, from other cartilages; when 

 dried, and exposed to the action of the atmosphere, they are^, 

 seen to consist of an immense number of small thin plates, placed 

 end to end, and separated by deep fissures. M. Herissant de- 

 scribes these plates as interlaced one with another, and forming 

 a kind of spiral, the regularity of which is interrupted by small 

 cartilaginous projections, uniting the plates to each other.* 

 These cartilages have a grest disposition to ossify, which is ma- 

 nifested in most individuals somewhat advanced in life. The 

 ossification begins in their centre, and advances to the circum- 

 ference, and is always preceded by a yellowish tinge. When 

 they are fully ossified, like the ribs, they are cellular within, 

 and compact externally, and are continuous with the ribs, there 

 being no interval: in such cases, the distinction from the ster- 

 num is generally kept up by the preservation of the joint, with 

 the exception of the first, which is fused into it. The complete 

 ossification of the first cartilage is not uncommon; the others, 

 though there is generally in old persons a considerable deposite 

 of bone in them, are seldom fully ossified. In neither case, 

 however, is it common to see such a perfect continuity of bone 

 between the rib and sternum, that the junction may not be dis- 

 solved at one point or another of this space by the action of 

 boiling water: at least, after very numerous observations on this 

 subject, I. do not remember to have met with a single instance 

 of it. 



* Acad. des Sciences, an. 1748. 



