u I launch Bone, &c. [Book IX, 



gradually ofiify, and the marks of the original reparation 

 difappear, fo that they become one irregular bone. 

 They ft ill, however, retain the names of ileum, ifchium, 

 and pubis, by which their divifions were originally dif- 

 tihguimed, and are defcribed as three different bones, 

 by *-he generality of anatomifts. The offa innominata 

 are connected pofteriorly to the os facrum, by a firm 

 cartilaginous fubftance. 



The os ileum or haunch-bone, forms the higheft and 

 moft confiderable part of the os innominatmn. The 

 external fide of the ileum is unequally convex, and is 

 called its dorfum : the internal concave furface is by 

 fome authors named its cofta. The fernicircular edge 

 at the higheft part of this bone, which is tipped with 

 cartilage in the recent fubject, is named the fpine. 

 This has two confiderable projections ; one anterior, 

 and the other pofterior, which is the larger of the two. 

 Thefe ends of the fpine being more prominent than 

 the furface of the bone below them, are therefore called 

 the anterior and pofterior fpinous procefles. Below 

 the anterior fpinous procefs another protuberance pro- 

 jects, which by its fituation may be diftinguifhed from 

 the former, by adding the epithet of inferior. Between 

 thefe two anterior procefTes, the bone is hollowed. 

 Below the pofterior fpinal procefs a fecond protube- 

 rance of the edge of this bone is alfo to be obferved, 

 which is clofely applied to the os facrum. Under this 

 laft procefs a ccnfiderable niche is oblervable in the os 

 ileum j between the fides of which and the ftrong liga- 

 ment which is ftretched over from the os facrum r.o the 

 /harp-pointed procefs of the os ifchium of the recent 

 fbbject, a large hole is formed, through which the 

 wnufculus pyriformis, the great fciatic nerve, and the 

 pofterior crural veffels, pafs, and are protected from 

 compreffion. The internal furface of the os ileum is 



concave 



