128 THE BONES. 



it rests on the sacrum, it becomes widened, as it also does in its posterior 

 portion, which is inflected inwards to be united, on the median Hne, with the 

 OS innominatum of the opposite side. 



It is divided, in the foetus, into three distinct pieces, joined by cartilage in 

 the centre of the cotyloid cavity, which they concur in forming. Although they 

 soon become consolidated into a single piece, it is customary to describe them as 

 so many separate bones by the names of ilium, pubis, and ischium. 



Ilium (Figs. 83, 84). — The ilium — a flat and triangular bone, curved on itself, 

 directed obliquely downwards, backwards, and outwards — forms the anterior 

 portion of the coxa which corresponds with the sacrum. It is the most consider- 

 able of the three divisions, and has two faces, three borders, and three angles or 

 processes. 



Faces. — The external or superior face (Fig. 83), studded Avith some muscular 

 imprints, is excavated on both sides, and is named the external iliac fossa. The 

 internal or inferior face offers for study : 1. An external portion, smooth, and 

 crossed by some vascular grooves ; this is the iliac surface, which is replaced in 

 Man by an excavation called the internal iliac fossa. 2. An internal portion, 

 roughened and uneven, presents, posteriorly, the auricular facet — an irregular 

 diarthrodial surface, elongated from side to side, a little oblique in front and 

 inwards, and responding to an analogous surface on the sacrum. 



Borders. — The anterior border, or crest of the ilium, is slightly concave, and 

 bears a roughened lip for muscular insertion. The external border is thick, 

 concave, and furrowed by vascular fissures ; it presents, inferiorly, the nutrient 

 foramen. The internal border is thin and concave, particularly in its posterior 

 part, which constitutes the great sciatic notch. 



Angles. — The externcd angle, or anterior and superior spinous 2)rocess, is thick, 

 wide, and flat, and bears four tuberosities : two superior and two inferior. The 

 internal angle, or posterior and siqjerior sp)inous j^rocess, represents a rugged tube- 

 rosity curved backwards and upwards. The posterior — or cotyloid angle — is pris- 

 matic and very volimiinous. It exhibits : 1. Behind, a wide concave articular facet, 

 which forms part of the cotyloid cavity. 2. Above this cavity, the supra-cotyloid 

 crest, represented in Man by the ischiatic spine. This is an eminence elongated 

 from before to behind, sharp on its summit, smooth inwardly, roughened out- 

 wardly, and continuous by its anterior extremity with the internal border of the 

 bone. 3. Outwardly, two deep imprints for the insertion of the rectus femoris 

 muscle. 4. In'front and inwards, the ilio-2^ectineal spine, a small elongated pro- 

 minence forming the most salient point of a kind of ridge {linea ilio-pectinea) that 

 insensibly subsides above on the inner face of the ilium, and is continued below 

 by the anterior border of the pubis. 



Of the three angles of the ilium, the first is also termed the angle of the 

 haunch, and the second the angle of the croup. 



Pubis (Fig. 83). — Situated between the ilium and ischium, elongated from 

 side to side, flattened above and below, and irregularly triangular, the pubis — the 

 smallest of the three divisions — is divided, for convenience of description, into 

 two faces, three borders, and three angles. 



Faces. — The superior, smooth and concave, concurs in forming the floor of 

 the pelvis. It shows one or two nutrient foramina. The inferior is roughened, 

 and marked throughout its length by a wide channel which reaches the bottom 

 of the cotyloid cavity. This fissure lodges the pubio-femoral ligament and 

 a very large vein. 



