PLATE XXVII. 

 THE BUTTOCK, GLUTEUS MINIMUS, &c. 



JpiB " 



In this dissection the gluteus maximus has been entirely removed from its origin 

 from the sacro-sciatic ligament, Ac., in order to show the plexiform arrangement of the 

 posterior primary branches of the sacral nerves, which lie in the ligament covered over by 

 its superficial fibres. The gluteus medius has also been divided and the ends turned 

 aside in order to expose the minimus and the tensor vaginae femoris, the gluteal nerve 

 and deep part of the gluteal artery. Some little difficulty will be experienced in separat- 

 ing the anterior fibres of the medius from those oi the minimus in front and below, 

 owing to their being blended. 



The superior and inferior gemelli are shown as one continuous muscular sheet lying 

 under the obturator internus tendon, and arising from the edge of the cartilage-covered 

 surface over which the tendon glides : this is the more usual condition in muscular 

 subjects, but often the muscle sub- 

 stance is absent in the centre, and then 

 the muscles have been rightly described 

 as two superior and inferior gemellus. 



The dissector should also note that 

 the tendon of the obturator lies on its 

 deep surface next the bone, which is here 

 grooved and covered by cartilage. 



The accompanying diagram shows * atetl t, r 

 more clearly than a description the dis- f"" 

 tribution and plexiform arrangement of 

 the posterior primary divisions of the 

 sacral nerves. As a rule, the three first 

 external branches only become cutane- 

 ous, but the fourth may do so ; the inter- 

 nal branches of the first three supply the 

 multifidus spinre. The fourth usually 

 joins the fifth and the coccygeal to form 

 a nerve twig, which is lost in the tissue 

 at the'back of the coccyx. 



Note on the Crucial Anastomosis. 

 At the back of the thigh in the neigh- 

 bourhood of the quadratus femoris there 

 is usually described a cruciform anastomosis, composed of the sciatic from above, the 

 internal circumflex from in front, the first perforating from below and the external 

 circumflex coining round below the trochanter through the fibres of the vastus externus ; 

 as thus described it is not often seen. There are generally two large anastomoses at 

 the. back of the thigh, one between the sciatic, gluteal, and internal circumflex in the 

 digital fossa, and another usually just beneath the edge of the hamstrings formed of the 

 sciatic first perforating and internal circumflex. The first perforating sends a branch 

 through the gluteus maximus into the vastus externus, and this anastomoses with the 

 external circumflex ; but the latter does not usually come round to the back of the 

 thigh. 



S antonor 

 primary brnohs 



