THE PELVIS. 



235 



Appears about 

 later end of 2nd 

 m. of foetal life 



Appears about 15 

 years ; fuses 22-25 

 years 



the pubis can all be distinguished in front, though overlain by a considerable quantity of fat, 

 whilst the position of the tuberosities of the ischia, when uncovered by the great gluteal 

 muscles in the flexed position of the thigh, can readily be ascertained. In the perineal region 

 the outline of the pubic and ischial rami can easily be determined by digital examination. 



Ossification commences in the ilium about the ninth week of intra-uterine life; 

 about the fourth month a centre appears below the acetabulum for the ischium, the os 

 pubis being developed from a centre which appears in front of the acetabulum about the 

 fifth or sixth month. At birth the form of the ilium is well defined ; the body and part 

 of the tuberosity of the ischium are ossified, as well as the superior ramus and part of 

 the body of the os pubis. All three parts enter into the formation of the sides of the 

 acetabulum, and by the 

 third year have con verged 

 to form the bottom of that 

 hollow, being separated 

 from each other by a tri- 

 radiate piece of cartilage, 

 in which, about the 

 twelfth year, independent 

 ossific centres make their 

 appearance, which may 

 or may not become fused 

 with the adjacent bones. 

 In the latter case they 

 unite to form an inde- 

 pendent ossicle, the os 

 acetabuli, which subse- 

 quently fuses with and 

 forms the acetabular part 

 of the os pubis. By the 

 age of sixteen the ossifica- 

 tion of the acetabulum is 

 usually completed, whilst 



the rami of the ischium At Birth - About 12 or 13 y ear s- 



and os pubis commonly FIG. 233. OSSIFICATION OF THE HIP BONE. 



unite about the tenth 



year. Secondary centres, seven in number, make their appearance about the age of 

 puberty, and are found in the following situations : one for the anterior inferior iliac spine ; 

 one for the ventral two-thirds of the iliac crest and the anterior superior iliac spine 

 which grows backwards, one for the posterior superior iliac spine and dorsal third of the 

 iliac crest which grows forwards these two unite about the twentieth year ; a scale-like 

 epiphysis over the tuberosity of the ischium ; a separate epiphysis for the spine of the 

 ischium ; (?) a point for the tubercle and another for the angle of the os pubis. Fusion 

 between these and the primary centres is usually complete between the twenty-second and 

 twenty-fifth years. Le Damany states that the proportionate depth of the acetabular 

 cavity at the sixth month* of foetal life is greater than at birth. In the third year a rapid 

 increase in its depth again takes place correlated with the assumption of the erect position. 



Parsons (Journ. Anat. and Physiol, vol. xxxvii. p. 3 15) regards the ischial epiphysis as 

 the homologue of the hypo-ischium in reptiles, and suggests that the epiphysis over the 

 angle of the pubis may represent the epipubic bone of marsupials. 



Appears about 

 4th m. of foetal 



Appears about 15 

 years ; fuses 22- 

 25 years 



At Birth. 



Appears about 

 15 years ; fuses 

 22-25 years 



Appears about 

 12 years 



Appears 

 .^ about 18 

 years 

 Appears 

 about 18 



Unite about 10 years 



The Pelvis. 



The pelvis is formed by the union of the hip bones with each other in 

 front, and with the sacrum behind. In man the dwarfed caudal vertebrae 

 (coccygeal) are curved forwards and so encroach upon the limits of the pelvic 

 cavity inferiorly. The pelvis is divided into two parts by the ilio-pectineal lines, 

 which curve forwards from the upper part of the lateral parts of the sacrum 

 behind to the roots of the pubic tubercles in front. The part above is called 

 the pelvis major, and serves by the expanded iliac fossae to support the abdominal 

 contents; the part below, the pelvis minor contains the pelvic viscera, 

 and in the female forms the bony canal through which at full term the fostus is 

 expelled. 



