THE FEMUR 97 



It is almost circular in the mare, semi-elliptical in the stallion, and faces ob- 

 liquely downward and forward. It has two principal diameters. Of these, the 

 conjugate or sacro-pubic diameter (Conjugata) is measured from the sacral prom- 

 ontory to the anterior end of the symphysis. The transverse diameter (Diameter 

 transversa) is measured at the greatest width, i. e., just above the psoas tubercle. 



The posterior aperture or outlet (Apertura pelvis caudalis) is much smaller 

 and is very incomplete in the skeleton. It is bounded above by the third coccygeal 

 vertebra and below by the ischial arch; in the fresh state it is completed laterally 

 by the sacro-sciatic ligament and the semimembranosus muscle. 



The axis of the pelvis is an imaginary line drawn through the centers of the 

 inlet, cavity, and outlet. 



Sexual Differences. — Marked differences exist in the size and form of the pel- 

 vis in the two sexes. The average conjugate diameter is al)out 9} 2 inches (ca. 23 to 

 24 cm.) in the mare, 73^^ inches (ca. 18 to 20 cm.) in the stallion. The transverse 

 diameter of the inlet averages about 9 inches (ca. 22 to 23 cm.) in the mare, and 8 

 inches (ca. 20 cm.) in the stallion. The obliquity of the inlet is greater in the female; 

 the difference is indicated l)y the fact that a vertical plane from the pccten cuts 

 the fourth sacral segment in the female, the second in the male. The outlet is 

 also larger in the mare, the ischial arch being about one-third wider than in the 

 stallion. The cavity is much more roomy in the female; the transverse diameter 

 between the middles of the superior ischiatic spines is about 8 inches (20 cm.) 

 in the mare, 6 inches (15 cm.) in the stallion. The pubic part of the floor in the 

 female is concave and lies considerably lower than the ischiatic part, which is wide 

 and relatively flat. In the stallion the pubis is very thick centrally, and this part 

 of the floor is convex, while tlie ischial part is relatively narrow, and is concave from 

 side to side. The obturator foramina are correspondingly larger in the female. 

 The ilium is shorter, and the greater sciatic notch deeper and narrower in 

 the male. The pelvis of the gelding, when castration has been performed early, 

 resembles that of the mare; otherwise the male characters appear to be retained 

 to a large degree. 



THE FEMUR 



The femur or thigh ])one (Os femoris) is the largest and most massive of the 

 long bones. It extends ol^liquely downward and forward, articulating with the 

 acetabulum above and the tibia and patella below. It presents for examination a 

 shaft and two extremities. 



The shaft or body (Corpus femoris) is in general cylindrical, but flattened 

 behind, and larger above than below. The anterior and lateral surfaces are con- 

 tinuous and strongly convex from side to side; there is often a central vertical 

 rough line on the proximal part, but otherwise these surfaces are smooth. They 

 are covered by the quadriceps femoris muscle. The posterior surface is wide, flat, 

 and smooth in its proximal fourth. Below this part there is a rough elevation 

 externally for the attachment of the femoral tendon of the biceps femoris, and a 

 rough line internally to which the quadratus femoris is attached. The middle 

 third is narrower, and is rough for the attachment of the adductor muscle. Just 

 below this area an oblique groove crosses the surface, indicating the position of the 

 femoral vessels. The internal border bears on its proximal part the internal 

 trochanter or trochanter minor, a thick rough ridge, to which the ilio-psoas muscle 

 is attached. From this a rough line curves up to the front of the neck and indicates 

 the limit of the attachment of the vastus internus muscle. A narrow rough area 

 about the middle gives attachment to the pectineus muscle, and the nutrient 

 foramen is usually found just in front of this mark. The supracondyloid crest is 

 situated below the groove for the femoral vessels, and gives origin to the inner head 

 7 



