DISSECTING MANUAL. 



coccyx and lower sacrum. It is divisible into four parts ac- 

 cording to its termination, viz. : pubo-rectalis, inserted at cen- 

 tral point of perineum; pubo-coccygeus, inserted at anus and 

 ano-coccygeal raphe; ilio-coccygeus and ilio-sacralis, inserted 

 at sacrum and coccyx. [440] 



Ischio-coccygeus. This overlaps the posterior border of the 

 preceding. Origin; ischial spine; small sacro-sciatic ligament. 

 Insertion; sides of lower two sacral and upper two coccygeal 

 vertebra?. The visceral pelvic fascia separates it from the 

 rectum. [441] 



NERVES. 



Posterior Spinal Nerves. Lower Thoracic. The external 

 cutaneous branches supply the skin of the loin and (two 

 lowest) buttock. [613] 



First , Second, and Third Lumbar. These divide into internal 

 and external branches. The internal branches supply the deep 

 muscles of the back. The external (cutaneous) branches de- 

 scend, pierce the vertebral aponeurosis posteriorly above the 

 iliac crest, and supply the skin from the midline above the iliac 

 crest to below and behind the great trochanter. [613] 



Fourth and Fifth Lumbar. These (usually) supply only the 

 longitudinal muscles of the back. A branch of the fifth may 

 join the first sacral. [613] 



First, Second, and Third Sacral. Loops between them, often 

 joined by branches of the fifth lumbar and fourth sacral, form 

 the Posterior sacral plexus on the back of the sacrum. From 

 the loops spring internal (muscular) branches to the Multi- 

 fidus spinae; and external cutaneous branches, piercing the 

 sacro-sciatic ligament and Gluteus maximus, to the skin on the 

 back of the sacrum and buttock near by. [613] 



Fourth and Fifth Sacral, and Coccygeal. These unite as the 

 Posterior sacro-coccygeal nerve, which pierces the sacro-sciatic 

 ligament to supply the skin over the coccyx. [614] 



Anterior Spinal Nerves. Seventh to Eleventh Thoracic. At 



[1981 



