Chap. 7-] 'fhe Pelvis.' n 



the thorax ; to render the cavity of the thorax larger 

 or fmaller in breathing -, to protect the vifcera of the 

 thorax ; to give origins and infertions to a variety of 

 mufcles ; and to fupport the mammae or breads. 



The pelvis, fo called from its reiemblance to a bafin, 

 conftitutes the -lowed part of the trunk. Its pofterior 

 part is formed by the os facrum, and its lateral and an- 

 terior parts by the ofia innominata. 



The os facrum may be ccnfidercd as a continuation 

 of the fpine; and fome anatomifcs have called both, 

 this bone and the oscoccygis by the name of thefalfe 

 vertebras. The os facrum is a large thick bone, of a 

 triangular form j its broadeft part is placed upperrnod, 

 and its narrowed is turned downwards and inwards. 

 The poderior furfaee of this bone is convex, the an- 

 terior concave. The two lateral margins of it are in- 

 crufted with cartilage, by the help of which it is im- 

 moveably connected with the offa innominata. In the 

 middle of this bone there is a canal for the fpinal mar- 

 row, correfponding with that in the vertebrae of the 

 fpine ; and on the anterior furfaee there are ten per- 

 forations, for the paflage of as many nerves. On the 

 poderior part there are many protuberances, which, 

 like the prbceffes of the vertebrae, ferve for the infer- 

 tion of mufcles,. 



The os coccygis is a fmall bone of a pointed fhape, 

 adhering to the lower part of the os facrum. The os, 

 coccygis is in infancy compofed of feveral pieces of 

 bone, which coalefce, however, in the adult date. It 

 may.be confidered as a continuation of the os facrum, 

 and is bent in the fame direction with that bone. 



Theoffa innominata, which form the fides and fore 



part of the pelvis, are two large broad bones, which iri 



infancy confid each of them of three clidinct pieces $ 



but as we advance in life, the intermediate cartilages 



J 2 -gradually 



