STRAIN OF PSO^ MUSCLES. 243 



regions, originating at the heads of the last ribs and last dorsal 

 vertebrae, extending in a backward direction under the bodies of 

 the lumbar vertebrae to the ilio-pectineal eminence on the brim 

 of the pelvis, and the internal trochanter of the femur. Their 

 action is to bend the haunch upon the pelvis, to draw it forward 

 in progression, or wliile the hind quarters are stationary and 

 fixed points, their action produces that appearance called 

 " roached back." 



It is important to remember the action of these muscles, 

 for when injured they cease to act, and the haunch will be 

 thrown into the opposite condition of " roached back ; " and 

 from this circumstance the injury may be readily distinguished 

 from azoturia. 



Strain of these muscles is caused by injury, such as " being 

 cast in the stall," or by any other accident capable of producing 

 violent extension of them ; hence arises the difficulty of deter- 

 mining between it and " broken back." It may, however, be 

 distinguished from the paralysis of broken back by the power of 

 flexing and extending the limbs being still retained by the ani- 

 mal whilst it is lying down ; there may be inability to rise from 

 the ground, as the psose muscles assist very materially in that 

 operation ; but when raised by means of slings from the recum- 

 bent position, and when the hind feet are firmly placed upon 

 the ground, the horse is able to stand moderately well, and 

 command the movements of the limbs to some extent, although 

 there is always a tendency to knuckling over at the fetlock- 

 joints. 



The muscles of one side may be injured ; in such a case the 

 loss of power is limited to one side only. 



If the injury be not sufficiently severe to destroy the power 

 of rising, it will be seen that, when the horse is made to walk, he 

 drags his limbs or trails them to some extent. There is scarcely 

 any elevation of the feet or flexion of the joints, and a great 

 tendency is shown to knuckle over at every step. 



Examination per rectum will reveal heat, tenderness, and 

 swelling under the spine ; and in the majority of cases that 

 have come under my observation, external swelling around the 

 rectum and perinseum, or vagina, if tlie patient be a mare, will 

 make its appearance in the course of a few hours after the 

 accident. 



