Etiology and Occurrence.--This is a comparatively rare injury in the horse because of the protection afforded the femur by the heavy musculature. Fragilitas of the bone probably exists in many cases when fracture of its diaphysis occurs. It is generally conceded that the neck of the femur is rarely broken because of a lack of constriction in this part, but fracture of the trochanters has been recorded rather frequently. However, Lienaux and Zwanenpoete[38] state that fracture of the neck of the femur is of frequent occurrence in Belgian colts. Tapley[39] reports in the Veterinary Journal (English) fracture of the head and internal trochanter of the femur and patellar luxation occurring simultaneously affecting a mule. In this case the mule was found decumbent on a concrete floor. After three weeks, the subject was destroyed and autopsy revealed rupture of the left pubiofemoral ligament, tearing with it a portion of the articular surface of the femur. The internal trochanter was also fractured in four small pieces. In this case it is fair to suppose that the mule in trying to regain footing on a slippery floor violently abducted the legs and fracture resulted. It is possible also that a temporary luxation of the patella took place first and caused the animal to struggle in such manner that fracture followed. [Illustration: Fig. 46--Oblique fracture of the femur of a 1,500 six-year-old draft horse. Showing shortening of bone, owing to a lateral approximation of the diaphysis because of muscular contraction. Photo by Dr. Edward Merillat.] Symptomatology.--According to Cadiot and Almy,[40] "regardless of the location of femoral fractures, the subject is usually intensely lame, the animal frequently walking on three legs--fractures of the diaphysis are characterized by an abnormal mobility." As a rule, crepitation is to be recognized in fractures of the shaft of the bone, by passively moving the leg to and from the medial plane (adduction and abduction). Fracture of the trochanter major is signalized by local swelling and evidence of pain; the forward stride is shortened because this movement tenses the tendon of the gluteus major (maximus) which is attached principally to the trochanter. [Illustration: Fig. 47--Same bone as in Fig. 46 after about six months' treatment. In this case Dr. Merillat employed a weight to counteract muscular contraction. It is noticeable that very little provisional callus has formed in this case, and in spite of unusual ingenuity and good facilities for caring for the subject, union of bone did not occur.]