THE PELVIS. 



Ridges? transversely across both surfaces, mark the union of its original 



segments. 



8 Anterior Sacral Foramina, for the anterior sacral nerves. 

 8 Grooves? shallow and broad, for the aforesaid nerves. 

 Promontory, at its junction with the last lumbar vertebrae. 

 8 Posterior Sacral Foramina, for the posterior sacral 



nerves. 

 Tubercles, representing the spinous processes of the 



segments. 

 Groove, posteriorly, on each side of the spinous 



tubercles. 

 2 Cornua, at the posterior inferior portion of the 



bone. 

 Auricular Surface? on each side, articulates with 



the ilium. 



Notch, laterally and inferiorly, for the 5th sacral nerve. 

 Base, 2 has all the characteristics of the lumbar vertebrae, with the last of 



which it articulates. 



Apex}* has an oval surface for articulation with the coccyx. 

 Sacral Canal, the continuation of the spinal, is incomplete posteriorly at its 



lower end. It transmits the Cauda Equina ; into it open the sacral fora- 



mina laterally. 



Describe the Coccyx. It consists of 4 or 5 rudimentary vertebrae coalesced 

 into a triangular bone, the base 1 of which articulates with the apex of the 

 sacrum. Its posterior surface is rough for muscles and liga- 

 ments, its anterior surface is smooth and marked by ridges at 

 the junction of its constituent vertebras. It presents the fol- 

 lowing points. 



2 Cornua? superiorly, articulating with the sacral cornua 

 to form foramina for the 5th sacral nerves. 



Apex, is sometimes bifid and turned to one side. 



Describe the Ossa Innominate. The unnamed bones are placed one on 

 each side of the osseous pelvis, and are each formed by the union, about 

 puberty, of 3 bones, the ilium, ischium, and pubes. The innominate bone 

 as a whole presents the following points, viz. 



Acetabulum, or cotyloid cavity, receives the head of the femur. It is situ- 

 ated at the junction of the 3 bones, the ilium and ischium each forming 

 about two-fifths, and the pubes one-fifth of it. A depression in its centre 

 lodges a mass of fat containing vessels for the nourishment of the synovia) 



FIG. 21. 



