CHAPTER V 

 THE LOWER EXTREMITY AND PELVIS 



THE bony pelvis, which, covered by soft tissues, forms the lower support of the 

 abdominal contents, is formed by two ossa innominata fixed behind to the sides of 

 the sacrum and meeting in front at the symphysis. It forms a firm and strong base 

 on which the trunk can rest, and through which its weight can be transferred to the 

 free limbs below. 



The sacrum and coccyx have been described already (p. 38), but it is necessary to 

 give a short description of the various parts of the innominate bone before considering 

 the pelvis as a whole. 



OS INNOMINATUM. 



A large irregular bone that helps to form the bony pelvis in conjunction with its 

 fellow and the sacrum. It articulates at its upper and back part with the side of the 



sacrum, below and in front with its fellow in the middle 

 line, and with the femur externally. The bone is formed by 

 the fusion of three separate main pieces : these are (Fig. 95) 

 the Ilium above, the Ischium below and behind, and the 

 Pubis below and in front. Where the three parts meet is 

 placed the acetabulum, on the outer side, for articulation 

 with the femur, so that the articular surface of this cavity is 

 composed of portions of all three parts. The three parts 

 are joined only by cartilage till just before puberty, so that 

 the following description applies to the adult bone. 



Looked at from the outer side (Fig. 96) the bone shows, 

 below its middle, the large and deep acetabulum to receive 

 the head of the femur, surrounded by the prominent aceta- 

 bular rim, best marked behind and above. The wall of the 

 cavity is deficient below, constituting the cotyloid notch. 



Above the acetabulum is the wide outer surface of the 

 ilium (dorsum ilii) for the gluteal muscles, and their areas 

 of origin are marked on the surface by the upper, middle, 

 and lower curved lines, due to the presence of tendinous fibres on the surfaces of the 

 muscles. Above, the bone terminates in the thick crest of the Ilium, and this ends in 

 front and behind in the anterior superior and posterior superior spines : below these 

 spines are notches which separate them from the anterior and posterior inferior spines 

 of the Ilium. Below the anterior inferior spine is another ill-defined notch and the 

 ilio-pectineal eminence, which marks the junction of Ilium and pubis : below the 

 posterior inferior spine is the deep great sciatic notch, and near the front border of this 

 notch, on the base of the wall of the acetabulum, is another rounded thickness which 

 marks the junction of Ilium and Ischium. 



The body of the Ischium is the mass of bone below and behind the acetabulum, 

 and forming part of this cavity : this is connected by an upper ramus with a large 



FIG. 95. To show the 

 three divisions of the 

 innominate bone which 

 fuse to form it about 

 puberty ; the thick lines 

 are cartilage. 



