33 



nerve trunk lies on the outer or lateral surface of the sacro-sciatic ligament 

 and is not very liable to be mutilated. Two smaller nerves however, the N. 

 pudendus (PI. V, 57) and the N. haemorrhoidalis (PI. V, 60) which originate 

 from the 2d, 3d, and 4th or from the 3d and 4th, only, sacral nerves lie on 

 the inner or pelvic surface of the sacro-sciatic ligament or else are imbedded 

 in its substance. Each of these two nerves is from one-half to one centi- 

 meter in width but is so thin, and in color so closely resembles the liga- 

 ment that it is liable to be overlooked and removed along with the 

 ligament. 



A. iliaca interna (PI. V, 34) is a very large vessel and arises from the aorta 

 close to the intervertebral disc between the 5th and 6th lumbar vertebrae. 

 It runs under the wing or transverse process of the sacrum, then turns 

 ventrally and extends along the pelvic surface of the shaft of the ilium to 

 near the psoas tubercle of the ilium, where the vessel divides into its two 

 terminal branches — ^the A. circumflexa femoris lateralis (iliaco-femoral 

 artery) and the A. obturatoria. To demonstrate this, remove a portion 

 of the overlying V. iliaca interna. 



Branches of the A. iliaca interna. 



(i) The last one of the six lumbar arteries arises from the dorsal side 

 of the A. iliaca interna and passes into the spinal canal through the inter- 

 vertebral foramen between the last lumbar vertebra and the sacrum. 



(2) A. pudenda interna (PL V, 37), already described. See p. 30. 



(3) A. sacralis lateralis (PI. V, 35). Remove the overlying V. sacralis 

 lateralis. The A. sacralis lateralis arises from the iliaca interna close to 

 the lumbo-sacral articulation. It extends along the sacrum ventral to the 

 sacral foramina and the nerves that emerge from them. At the third 

 sacral vertebra the artery divides into two branches — A. coccygeus lateralis 

 and the much larger A. glutea posterior. Trace the A. coccygeus lateralis 

 some distance along the tail to which it is distributed. The dissection 

 of the A. glutea posterior must be deferred until the gluteal nerves are 

 dissected. See p. 38. 



(4) A. iliolumbalis arises at a right angle from the lateral side of the 

 iliaca interna, crosses the ventral surface of the ilium beneath or dorsal to 

 the Mm. psoas magnus and iliacus to which it gives small branches. Tran- 

 sect the M. iliacus opposite the artery. Draw aside the iliacus and the 

 psoas magnus and trace the artery to where it crosses the external border 

 of the ilium a little behind the external angle. Its terminal branches which 

 will be demonstrated later, enter the gluteus medius and the tensor fasciae 

 latae. 



