A dissection of the Rt L5 dorsal ramus and the branches of the L4 dorsal ramus

[파란별님]

 
 A dissection of the right L5 dorsal ramus and the branches of the L4 dorsal ramus, viewed dorsally from the right, peering over the dorsal segment of the right iliac crest.
Abbreviations:
 PF  = posterior  sacral  foramen;
 ZJ  =zygapophysial  joint;  TP = transverse  process;  dr  = dorsalramus; mb = medial branch;

ib = intermediate branch; lb =lateral branch; cb = communicating branch; mal = mamillo-accessory ligament.

The  medial  branches  of  the  dorsal  rami  at  segmental  levels  L1  to  L4  assume  a  constant  and similar course. Each nerve emerges from its intervertebral  foramen  and  enters  the  posterior  compartment of the back by coursing around the neck of the superior articular
process below the foramen 

 Still hugging the neck of the superior articular process, the  medial  branch passes  caudally  and  slightly  dorsally  to  disappear under  the  mamillo-accessory  ligament

Beneath  the  ligament,  the  nerve  hooks  medially around  the  caudal  aspect  of  the  root  of  the  superior  articular  process  to  enter  the  multifidus muscle.  Intermediate  and  lateral  branches  arise from  the  dorsal  ramus  at  the  same  point  as  the medial branch. These nerves run caudally and laterally,  across  the  transverse  process,  into  the longissimus  and  iliocostalis  muscles,  respectively

 At  the  L5  level,  the  anatomy  is  different. 

The L5  dorsal  ramus  is  much  longer  than  at  typical lumbar  levels.
From  the  L5-S1  intervertebral foramen, it runs along the groove formed between the ala of the sacrum and the root of the S1 superior  articular  process Opposite  the caudal  end  of  the  superior  articular  process, its medial  branch  hooks  medially around the caudal aspect

of  that  process, running deep to some fibrous tissue that constitutes the analog of 

the mamillo-accessory  ligament at this level 
 A  communicating  branch  to  the  S1  dorsal ramus  continues  the  longitudinal  course  of  the dorsal ramus.