THE JjUMBO-SACRAL PLEXUS. ST! 



These two branches communicate by deep or superficial anastomosing loops. 

 Before leaving the space between the sartorius and gracilis, they give some 

 slender filaments to these two muscles, particularly to the latter. Near their 

 origin, they even distribute some to the iJiacus. Becoming subcutaneous, theii 

 ramuscules cover the inner face of the thigh and leg ; the longest of these accom- 

 pany the saphena vein to the anterior aspect of the hock. 



It sometimes — indeed, most frequently — happens that the internal saphena 

 nerve and its accessory form only a single branch, the muscular or cutaneous divi- 

 sions of which otherwise comport themselves exactly like the above. This is 

 exemplified in the dissection represented in Fig. 473. 



3. Obturatoe Nerve (Fig. 473, 4). 



Situated underneath the peritoneum, to the inner side of the iliac vessels — which 

 it accompanies to the origin of the obturator artery — this nerve follows the latter 

 to the upper face of the pubes, and passes with it beneath the internal obturator 

 muscle, to traverse the obturator foramen. In this way it arrives outside the 

 pelvis, where it nevertheless remains deeply concealed by the muscular masses on 

 the internal aspect of the thigh. Its terminal ramification are expended in the 

 obturator externus, adductors of the thigh, pectineus, and gracilis. The branch 

 to the latter muscle is the longest ; it leaves the space between the pectineus and 

 graciUs, and descends backwards on the internal face of the muscle to which it is 

 distributed. 



B. Posterior Portion. 

 4. Small Sciatic or Anterior and Posterior Gluteal Nerves. 



The small sciatic nerve of the Horse is composed of several cords that issue 

 from the pelvis by the upper part of the great sciatic notch, and which have been 

 for a long time described as the anterior and posterior gluteal nerves. 



The anterior gluteal or ilio-musmlar nerves (Fig. 474, 2, 3, 4, 5) are four or 

 five in number, and arise either separately or in groups from the posterior portion 

 of the lumbo-sacral plexus. They appear to be more particularly furnished by 

 the two first sacral branches. All leave the pelvic cavity by the gi-eat sciatic 

 opening, along with the anterior gluteal vessels. The principal branches are lost 

 in the middle gluteal muscle. One of them (Fig. 474, 4) crosses the neck of 

 the ilium above the superficial gluteal muscle, and passes outwards to be dis- 

 tributed to the tensor vaginae femoris. The last, which is the most slender, 

 descends to the external surface of the superficial gluteus, and is distributed in 

 its substance (Fig. 474, 5). 



The posterior gluteal, or isrhio-muscular nerves (Fig. 474, 6, 6', 8), are usually 

 two in number — a superior and inferior. 



The first escapes through the great sacro-sciatic notch, along with the femoro- 

 popHteal nerves, and is situated on the external surface of the sciatic ligament. 

 It passes backward, between this ligament and the middle gluteus, to beneath 

 the anterior or croupal portion of the biceps femoris, in which it is distributed 

 by several filaments. Besides these, it gives : 1. In passing beneath the gluteus 

 middle, a slender, but constant filament to the posterior portion of that muscle. 

 2. Another, and more considerable branch, which bends round the posterior 

 border of that muscle, to be directed forward and outward to the superficial 

 gluteus 



58 



