112 THE SKELETON OF THE HORSE 
24 em.) in the mare, 7/4 inches (ca. 18.75 em.) in the stallion. The transverse 
diameter of the inlet is about the same as the conjugate in the mare, but is about 
8 inches (ca. 20 em.) in the stallion. The obliquity of the inlet or inclination of the 
pelvis (Inclinatio pelvis) is greater in the female; the difference is indicated by the 
fact that a vertical plane from the pecten cuts the fourth sacral segment in the fe- 
male, 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 ischiatie 
spines is about 8 inches (20 em.) 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 almost flat. In the stallion the pubis is very thick 
medially, and this part of the floor is convex, while the ischial part is relatively nar- 
row, and is concave from side to side. The obturator foramina are correspondingly 
larger in the female. The ilium is shorter, especially with regard to its shaft, and 
the greater sciatic notch is deeper and narrower in the male. The pelvis of the geld- 
ing, when castration has been performed early, resembles that of the mare; other- 
wise the male characters appear to be retained to a large degree. 
THE FEMUR 
The femur or thigh bone (Os femoris) is the largest and most massive of the 
long bones. It extends obliquely 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 (Corpus femoris) is in general cylindrical, but flattened behind, and 
larger above than below. The anterior, medial, and lateral surfaces are continuous 
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. Distal to this part there is a rough elevation laterally for 
the attachment of the femoral tendon of the biceps femoris, and a rough line medi- 
ally to which the quadratus femoris is attached. The middle third is narrower, 
and is rough for the attachment of the adductor muscle. Just distal to this area 
an oblique groove crosses the surface, indicating the position of the femoral vessels. 
The medial border bears on its proximal part the 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 posterior limit of the attachment of 
the vastus medialis muscle. A narrow rough area about the middle of the border 
gives attachment to the pectineus muscle, and the nutrient foramen is usually 
found just in front of this mark. The medial supracondyloid crest (Crista supra- 
condyloidea medialis) is situated below the groove for the femoral vessels, and gives 
origin to the medial head of the gastrocnemius. The lateral border is prominent | 
in its upper part, and bears at the junction of its proximal and middle thirds the | 
trochanter tertius;! this process is curved forward, and has a thick edge to which 
the tendon of the superficial gluteus muscle is attached. At the distal part is the 
supracondyloid fossa (Fossa supracondyloidea),? in which the superficial digital 
flexor arises; it is bounded laterally by a thick, rough margin, the lateral supra- 
condyloid crest (Crista supracondyloidea lateralis), to which the lateral head of the 
gastrocnemius muscle is attached. 
The proximal extremity (Extremitas proximalis) is large and consists of the | 
head, neck, and trochanter major. The head (Caput femoris) is placed at the 
medial side and is directed inward, upward, and somewhat forward. It is ap- 
proximately hemispherical and articulates with the acetabulum. It is cut ito 
1 Also termed the external trochanter. 2 Also termed the fossa plantaris. 
