THE LOWER LIMB 425 



(a) Two or three twigs from the external branches of the posterior 

 primary divisions of the first three sacral nerves. These external 

 branches form two sets of loops, one set being situated deeply on 

 the back of the sacrum, and the other set more superficially on the 

 posterior surface of the great sacro-sciatic ligament. It is from this 

 latter set of loops that the two or three cutaneous twigs are derived, 

 and their direction is chiefly outwards. 



{h) One or two t\\igs from the undivided posterior primary divisions 

 of the last two sacral nerves and the coccygeal nerve. These 

 divisions form a loop on the back of the sacrum, from which the 

 cutaneous twigs are derived, their distribution being confined to the 

 coccygeal integument. 



(c) Twigs from the so-called coccygeal plexus, which is situated 

 on the pelvic surface of the coccygeus muscle. These twdgs pierce 

 that muscle and the small sacro-sciatic hgament, as well as the 

 gluteus maximus, and are distributed to the coccygeal integument. 



2. Ulac Crest. — The cutaneous nerves in this situation from behind 

 forwards are also divisible into three sets. 



(fl) Three offsets from the external branches of the posterior 

 primary divisions of the first three lumbar nerves, which descend 

 over the Hiac crest, in front of the outer border of the erector spinae 

 muscle. 



(h) Ihac branch of the Uio-hypogastric nerve, which crosses the 

 ihac crest at the jimction of the middle and anterior thirds. 



(c) Undivided lateral cutaneous or ihac branch of the anterior 

 primary division of the twelfth thoracic (subcostal) nerve. This is 

 a large and long nerve which descends over the anterior part of the 

 ihac crest, i inch behind the anterior superior ihac spine, and is 

 distributed to the integument of the anterior part of the gluteal 

 region as low as the great trochanter. 



3. Outer and Lower Part of Gluteus Maximus. — The cutaneous 

 nerves appearing in this situation are branches of the posterior 

 division of the external cutaneous nerve, which is derived from the 

 lumbar plexus. 



4. Lower Border of Gluteus Maximus. — ^The cutaneous nerves met 

 with in this locahty are as follows : 



(a) Three or forn: recurrent branches from the small sciatic nerve, 

 which supply the integmnent over the lower and outer part of the 

 gluteus maximus. 



(6) Perforating cutaneous branch of the sacral plexus, more 

 particularly from the back of the second and third sacral nerves, 

 which supphes the integument ov^er the lower and inner part of the 

 gluteus maximus. 



Fasciae. — ^The superficial fascia is very thick, and loaded with 

 adipose tissue. It is continuous over the ihac crest with the super- 

 ficial fascia of the back of the trunk, and it contributes to the 

 prominence of the natal region. Between the ihac crest and the 

 upper border of the gluteus maximus there is a considerable 

 accession of adipose tissue to the deep siurface of the superficial 



