174 THE SURGICAL ANATOMY OF THE HORSE 



THE GLUTEAL NERVES 



These nerves are in two sets, designated respectively anterior and 

 posterior. Collectively they form what is sometimes referred to as 

 the small sciatic nerve. Both sets are given off by the lumbo- 

 sacral plexus, and leave the pelvic cavity by the greater sacro- 

 sciatic foramen in company with the gluteal vessels and the great 

 sciatic nerve. 



The nerves of the anterior set vary in number from three to five, and 

 their fibres are derived almost exclusively from the first and second sacral 

 roots of the plexus. They pass through the foramen mentioned in front 

 of the great sciatic nerve and beneath the gluteal arteries. Covering the 

 greater sacro-sciatic foramen we have the middle gluteus muscle, or 

 gluteus maximus, and in this muscle most of the filaments of this set are 

 expended. One of the nerves takes a course downwards and forwards 

 between the middle and deep gluteal muscles, lying on the latter ; crosses 

 the neck of the ilium, and then passes outwards to supply the tensor 

 vagina' femoris muscle. Another passes to the outer surface of the 

 anterior arm of the superficial gluteus, which it supplies. A third branch 

 passes downwards over the outer surface of the deep gluteus, and is 

 distributed to this muscle. The nerves of the anterior set are sometimes 

 termed the ilio-muscular nerves. 



In the posterior set there are two nerves, to which the name ischio- 

 muscular is sometimes applied. They leave the greater sacro-sciatic 

 foramen behind and above the great sciatic nerve, and lie on the outer 

 surface of the great sacro-sciatic ligament. The superior nerve passes 

 backwards on the ligament and between it and the middle gluteus 

 muscle to terminate in the biceps femoris. During its course, whilst 

 beneath the middle gluteus, it gives off a slender branch which 

 is distributed to the posterior portion of that muscle. A second and 

 much larger branch is detached which curves round the posterior 



