372 



DISSECTION OF THE BACK. 



may be traced inwards ; the inner branches are very slender and difficult 

 to be recognized. 



The lowest two nerves are very small, and are to be sought on the back 

 of the sacrum, below the attachment of the multifidus spinae. They are 

 not bifurcated like the others, but unite together, and with the coccygeal 

 nerve in loops. The fourth comes through a sacral aperture, the fifth 

 between the sacrum and coccyx ; and the coccygeal is still lower. 



SACRAL NERVES (fig. 120) The posterior primary branches of the 

 sacral nerves are five in number. Four issue from the spinal canal by the 

 apertures in the back of the sacrum, and the fifth between the sacrum and 

 the coccyx. The first three have the common division into inner and 

 outer pieces, like the other spinal nerves ; but the last two are undivided. 



* The first three nerves are covered by the multifidus spinae; and divide 

 regularly. 



The inner pieces (') are distributed to the multifidus ; and the last of 

 this set is very fine. 



The outer pieces ( 2 ) are larger, and have communicating offsets from one 

 to another on the back of the sacrum : further, the branch of the first 



Fig. 120. 



Muscles : 



A. Multifidus spin.-p. and 



B. Erector spinae : both cut. 



c. Gluteus maximus detached from its origin, and 



thrown down. 



D. Great sacro-sciatic ligament. 

 Nerves : 



5 I. Last lumbar. 

 1 S to 5 S, the five sacral nerves issuing from the 



sacrum. 

 1 c. The coccygeal nerve, escaping by the opening 



of the sacral canal. 



1. Internal offsets of the last lumbar and first three 



sacral (these are too large iu the cut) : and 



2. External offsets of the same nerves. 



3. Anterior primary branch, and 



4. Posterior of the coccygeal nerve. 



5. The nerve derived from the anterior primary 



branches of the lower sacral nerves, which 

 pierces the sacro-sciatic ligament. 



DISSECTION OF THE SACRAL NERVES (Loud. Med. Gazette, 1843). 



nerve is connected with the corresponding part of the last lumbar ; and 

 the branch of the third joins in a similar manner the sacral nerve next 

 below. After this looping they pass outwards to the surface of the great 

 sacro-sciatic ligament, where they join a second time, and become cuta- 

 neous. (DISSECTION OF THE BUTTOCK.) 



* Last two nerves (4 S and 5 $). These nerves, which are below the 

 multifidus, are much smaller than the preceding, and want the regular 

 branching of the others : they are connected with each other and the coc- 



