106 THE CAT. [CHAP. iv.' 



(3). Another, stouter, piece of bone curves first backwards from 

 the thigh-socket, then downwards and forwards till it meets 

 the pubis. This is the ISCHIUM (Fig. 46, t, and Figs. 65 and 

 66, p). 



The ilium has a slightly concave outer surface, the upper border 

 of which is termed the "crest" (c), and is somewhat convex and 

 arched. This surface is also called " gluteal" because the gluteal 

 muscles are attached to it. From the front end of the crest the 

 anterior border descends sharply to the pubis, a blunt prominence 

 (called the ilio-pectincal eminence) marking the point of junction. 

 Another prominence (the anterior spinoits process) projects from 

 the anterior border of the ilium near its summit. From the hinder 

 end of the crest of the ilium descends its posterior border, the 

 summit of which is marked by the posterior spinous process, separated 

 by a wide notch from a small marked prominence, called the spine 

 of the ischium (ip). 



The inner surface of the ilium is slightly concave, forming the 

 iliac fossa (il) and at its anterior and upper part is a rough irregular 

 space, called the auricular surface (ar), for articulation with the 

 sacrum. The ilium forms about the upper third of the socket for the 

 thigh-bone. 



The PUBIS, or pubic bone, forms the inner part of the thigh-socket, 

 joining the ilium above, and at its junction contributing to form the 

 ilio-pectineal eminence. It thence descends inwards (as a band of 

 bone flattened from without inwards, called the horizontal ramus) 

 till it meets with its fellow of the opposite side, when it turns sharply 

 backwards and downwards. The junction of the two pubes is termed 

 the symphysis (sp), and the part of each pubis next the syinphysis is 

 sometimes called the body ; thence the pubis runs outwards and 

 backwards, as a flattened band, till it meets the ramus of the 

 ischium. 



The ISCHIUM forms the outer and hinder part of the thigh-socket, 

 and indeed of the whole os innominatum. The body of the ischium 

 forms about two-fifths of the socket for the thigh, which cavity is 

 situated on its anterior and outer side. The body is broad, and sends 

 from its posterior upper margin a slightly marked process, called the 

 spine of the ischium (ip). Behind this, and behind the socket, the bone 

 contracts somewhat, and then expands again, the expansion having 

 a rough, outwardly projecting prominent surface, which is called the 

 tuberosity of the ischium (p) ; and it is the two tuberosities (of the 

 two ossa innominata) which support the body when in the sitting 

 posture (Fig. 64, t). Just below the tuberosity, the ischium sends 

 forth a flat band of bone (the ramus), which, curving forwards and 

 downwards, meets the bony band of the pubis spoken of above. 

 Between the spine and the tuberosity of the ischium the posterior, 

 upper margin of the bone is slightly concave. 



The socket for the thigh-bone (which has been so often referred 

 to) is called the acetabulum, or cotyloid cavity. It has a prominent 

 rim, except at the inner and lower part where the rim is interrupted 



