LUMBO-SACRAL PLEXUS 



705 



ilio-hypogastricus, detaches branches to the internal obhque muscle, and descends 

 the inguinal canal with the inguinal branch, to be distributed to the external genital 

 organs and the surrounding skin in the inguinal region. 



The ventral branch of the third lumbar nerve is connected by a small anasto- 

 motic branch with the second nerve and furnishes a root of the lumbo-sacral plexus. 

 It gives off a branch to the psoas muscles, an inguinal branch, and is continued 

 as the external cutaneous nerve. The inguinal branch (N. spermaticus externus) 

 passes backward in the substance of the psoas minor, from which it emerges under 

 cover of or near the circumflex 

 iliac vessels. It then runs ex- 

 ternal to and parallel with the 

 external iliac artery and de- 

 scends in the inner part of the 

 inguinal canal. It emerges at 

 the external ring with the ex- 

 ternal pudic artery and rami- 

 fies in the external genital 

 organs and the skin of the 

 inguinal region. The external 

 cutaneous nerve of the thigh 

 (N. cutaneus femoris lateralis) 

 runs backward in the sub- 

 stance of the psoas muscles 

 and emerges at the outer bor- 

 der of the psoas minor. It 

 then passes outw^ard and back- 

 ward on the iliac fascia and 

 accompanies the posterior 

 branch of the circumflex iliac 

 artery. With this vessel it 

 perforates the abdominal wall 

 by passing between the ex- 

 ternal oblique and the iliacus 

 a short distance below the 

 point of the hip, and descends 

 on the inner face of the tensor 

 fasciae latse (near its anterior 

 border) and ramifies subcuta- 

 neously in the region of the 

 stifle. 



The origin and disposition of 

 some of the foregoing nerves are 

 variable. In some cases the iho- 

 inguinal nerve ends in the psoas 

 major, and appears then to be ab- 

 sent. The mode of formation of 

 the inguinal nerves is verj' incon- 

 stant. The inner nerve mav arise . • 1 1 i 

 with one of the outer ones from a common trunk, or they may anastoniose. The mgmnal branch 

 of the ilio-inguinal nerve often receives a twdg from the ilio-hypogastnc nerve. 



The ventral branches of the fourth, fifth, and sixth lumbar nerves concur in 

 the formation of the lumbo-sacral plexus. 



Lumbo-sacral Plexus 

 This plexus (Fig. 451) results substantially from the union of the ventral 

 branches of the last three lumbar and the first two sacral nerves, but it derives a 

 45 



Pig. 525. — Superficial Nerves of Peit 

 VIC Limb and Posterior Part op 

 Trunk of Horse. 

 a. Cutaneous branches of sixteenth 

 and seventeenth thoracic nerves; 6, cuta- 

 neous branches of lumbar nerves; c, cu- 

 taneous branches of sacral nerves; d, 

 cutaneous branches of coccygeal nerves, 

 e. f, g, cutaneous branches of last inter- 

 costal, ilio-hypogastric. and iho-inguinal 

 nerves; g' , end of external cutaneous nerve 

 of thigh; h, posterior cutaneous nerve of 

 thigh: i, i, cutaneous branches of great 

 sciatic nerve; k, posterior cutaneous nerve 

 of the leg; I, superficial peroneal nerve, 

 TO, terminal part of deep peroneal nerve; n, external plantar nerve, 

 1, obliquus abdominis externus; 2, tensor fasciae latse; 3, gluteus 

 superficialis; 4, biceps femoris; 6, seniitendinosus; 6, anterior ex- 

 tensor; 7, lateral extensor; 8, flexor tendons; 9, great metatarsal 

 artery. (After EUenberger, in Leisering's Atlas.) 



