THE FEMUR 385 



spring in breaking the jars received by the hind extremity from tlie ground. 

 Its oblique direction, its comparatively short surface of attachment to the 

 sacrum, and its own great length show this most plainly, especially when 

 compared with the human pelvis, in which a very different 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 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 ischii, 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 glutei 

 muscles. Internally it is rough, and gives attachment to the strong car- 

 tilage and ligaments which bind it to the sacrum. The processes extending 

 forwards are called the spinous processes of the ilium (see Fig. 44). 

 Behind the neck the bone swells out slightly for the development of the 

 cotyloid (/corvArj, 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, apparently 

 intended to lighten the bone, being filled up by a strong membrane, the 

 obturator ligament. Above this opening is the ramus of the ischium, which 

 bone also enters into the composition of the hip joint as already described. 

 Posteriorly the ischium terminates in a rough protuberance, the tuberosity 

 (9-9, Fig. 32), which is the rounded projection felt and seen on each side the 

 root of the tail in the living horse. Below the foramen is the os pubis, the 

 anterior part of which is the ramus, and the small section of the cotyloid 

 cavity which it forms, while posterioi'ly the body unites with the os ischii, 

 to form, with the corresponding bones of the opposite side, the symphysis, 

 or connecting joint between them. 



By the conjunction of the two ossa innominata an oval ring is nearly 

 completed, the deficiency being supplied by the sacrum above. The 

 anterior margin of this ring is the brim of the pelvis, and it is upon the 

 size of this as compared with the foal that parturition is in general rendered 

 easy or difficult. 



THE FEMUR (ROUND-BONE) AND PATELLA 



The Os Femoris, the strongest and heaviest bone in the body, is situated 

 between the os innominatum and the tibia. It takes an oblique direction 

 from above downwards and forwards, and presents a central part or body, 



