228 



A MANUAL OF ANATOMY 



Acetabulum. — The superior pubic ramus is shut out from this cavity for 

 some time by a triangular portion of cartilage, called the pars acetabularis. 

 From its apex there is prolonged backwards a strip of cartilage {ilw-ischial) . 

 The entire cartilage resembles the letter Y, laid on its side. The open part 

 of the Y is directed forwards, and forms the pars acetabularis. The Y cartilage 

 has 3 secondary centres. One, called the acetabular centre, appears in the 

 i2th year in the pars acetabularis, and ossification is completed by the i^th 

 year. It then forms a distinct bone, called the OS acetabuli, which joins the 

 superior pubic ramus about the i6th year. 



Appears about the 15th Year, 

 and joins about 25 



Appears about the 15th Year, 

 and joins about 25 



Represents the 

 Os Acetabuli 



Appears about the 15th Year,, 

 and joins about 25 



- Appear about the 1 2th Year, 



and join about 18 

 Appears about the 15th Year, 

 and joins about 35. 



.. Appears about the 15th Year, 

 and joins about 25 



Join in the 8th Year 



Fig. 134. — Ossification of the Epiphyses of the Os Innominatum. 



The other two secondary centres for the Y cartilage appear about the 14/A 

 year, one of them in the ilio-ischial strip or stem of the Y; and the other at 

 the meeting of the two limbs and stem of the Y. The ossification of the 

 bottom of the acetabulum is completed from the i6tk to the \%th year. 



Other Secondary Centres. — ^These are as follows: (i) One for the crest, one for 

 the anterior inferior iliac spine, one (a thin scale) for the surface of the tuber 

 ischii, and one for the spine of the ischium, each of these centres appearing 

 about the i^th year ; (2) one for the pubic spine, and one for the pubic angle, 

 each of these two centres appearing about the 18/A year. These epiphyses 

 usually join about the 2$th year. 



The Pelvis. 



The pelvis is formed by the ossa innominata, sacnim, and 

 coccyx, the hip-bones constructing the anterior and lateral walls, 

 whilst the sacrum and coccyx lie in the posterior wall. It is 

 divided into two parts, called false pelvis and true pelvis, the 

 division being effected by a plane passing through the upper border 

 of the symphysis pubis, ilio-pectineal line, and sacral promontory. 



The false pelvis, which lies above this plane, is formed by the 

 iliac fossae, and constitutes a part of the abdomen proper. 



The true pelvis is situated below the plane referred to, and pre- 

 sents a brim or inlet, a cavity, and an outlet. The brim is formed 

 in front by the upper border of the symphysis pubis, behind by the 



