OBSTETRICS. 



OF THE BONES OF THE PELVIS. 



/ The pelvis is an irregular bony cavity, situated at the base of the 

 spinal column, and above the inferior extremities, with which it is 

 connected by muscles and articulations, and for which, as well as for 

 the muscles of the trunk, it constitutes " a point d'appui." 



When divested of its soft structures, this organ somewhat resem- 

 bles a basin, and hence its name; for the Greeks called it -TrsX-jl, a 

 wooden utensil of bowl-form ; the Latins from them derived the word 

 pelvis, which is the term generally adopted by English and American 

 writers. The French call it le bassin, the Italians el baci?io, all 

 which words have the same signification. 



In the adult, the pelvis consists of four parts, viz. : two ossa inno- 

 minata^ the os sacrum, and the os coccygis, but in early life they are 

 more minutely divisible. 



Each OS innominatum at an early period of intra-uterine life con- 

 sists of cartilage only. Subsequently bony depositions take place, 

 which at birth have coalesced so as to form three bones separated 

 by cartilage. The process of ossification continues till these three 

 bones meet in the acetabulum, two-fifths of which are formed by the 

 ihum, two-fifths by the ischium, and one-fifth by the pubis. 



The breadth of each os innominatum, from the anterior superior 

 spinous process to the posterior superior spinous process is six inches, 

 and the height, from the tuber ischii to the crest of the ilium, is seven 

 inches. 



Os ilium, hip, or haunch bone (Fig. 1), is the largest of the three 

 divisions of the os innominatum, and is uppermost in position. It has 

 an outer and an inner surface; the outer{^) is called dorsum, and is 

 irregularly convex, and marked by eminences and depressions afford- 

 ing attachments for the glutsei muscles. The i7iner(^°) is concave 

 and smooth, and is called venter ; it is occupied by the iliacus inter- 

 nus muscle. The lower portion, the base, or body,{^) is the thickest 

 part of the bone, and enters largely into the composition of the ace- 

 tabulum, a cavity for the reception of the. head of the femur. Just 

 above the base, the bone narrows into a kind of neck, from which 

 springs the ala or wing. The ala terminates superiorly in a ridge 

 running along its whole extent, called the crista ilii, or crest of the 



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