TUE PELVIS. 343 
formation prevails. In the horse it forms, with the sacrum, the first of a 
series of angles, the second being between it and the femur, the third at 
the stifle joint, and the fourth at the hock. 
In THE EMBRYO the three bones are quite distinct, the cartilaginous lines 
of separation being visible for some time after birth, running through the 
cup-like cavity which forms the socket of the hip joint. The portion 
Fic. 32.—PROFILE VIEW OF THE TWO Ossa INNOMINATA, 
1. 1. Wings of the iliac bones. 5. Antero-inferior spinous process of the left 
2. 8. Pubic bone. ilium. 
3. Ischiac bone. 6. The narrow part or neck of the ilium. 
4. 4. Supero-posterior spinous process of the 7. 7. Obturator holes (foramina). 
two ossa ilii. 9. 9. Tuberosity of each ischium. 
10. Acetabulum. 
lying above and in front of this cavity, and taking in also two-thirds of 
its own cup, is the os ilii. Posteriorly to the cavity, the bone is divided 
into two strong branches by a large opening, the obturator foramen, and 
that portion which lies above it is the os ischiz, while the lower division 
is the os pubis. It is needless to describe these bones separately. 
THE BONE AS A WHOLE may be considered as divided into two parts by 
the contracted neck which forms its middle. The anterior of them is 
hollowed out externally for the reception and attachment of the g)utei 
muscles. Internally it is rough, and gives attachment to the strong car- 
tilage and ligaments which bind it to the sacrum. ‘The processes extend- 
ing forwards are called the spinous processes of the ilium (see Fig. 99). 
Behind the neck the bone swells out slightly for the development of the 
cotyloid (korvAy, a cup) cavity, or acetabulum. This is nearly three inches 
in diameter, and is surrounded on all sides but that looking towards the 
obturator foramen by a prominent lip. ‘The interval is called the notch, 
and corresponding with it is a rough depression in the cotyloid cavity, 
where the cartilage is absent, and to which the round ligament of the 
hip is attached. Behind the cotyloid cavity is the obturator hole, appa- 
