1010 THE NERVOUS SYSTEM 



to the lumbar region, and many pass by the immediate peripheral branches to the 

 splanchnic nerves. 



Among those which descend to the lumbar region are pilo-motor fibres, vaso-motor 

 fibres, and secretory fibres to the lower limb, some vaso-constrictor fibres to the ab- 

 dominal blood-vessels, motor fibres to the circular, and inhibitory fibres to the longi- 

 tudinal muscle of the rectum. The latter enter the sympathetic trunk by the lower 

 thoracic nerves and pass in the lumbar peripheral branches to the aortic plexus, and 

 terminate around the cells of the inferior mesenteric ganglion. 



The fibres which pass through the thoracic ganglia to the splanchnic nerves are 

 mainly vaso-motor fibres to the abdominal blood-vessels; the majority of them 

 probably terminate around the cells of the ganglia in the coeliac (solar) plexus, but 

 those for the renal blood-vessels no doubt end in the renal ganglia. In addition to 

 all the above-mentioned fibres there are in the thoracic part of the sympathetic trunk 

 afferent (splanchnic sensory) fibres of both sympathetic and cerebro-spinal type, 

 passing towards the spinal ganglia and dorsal roots of the thoracic spinal nerves. 



THE LUMBAR PORTION OF THE SYMPATHETIC TRUNK 



The lumbar portion of each trunk lies on the fronts of the bodies of the vertebra? 

 along the anterior border of the psoas muscle, and nearer to the median line than the 

 thoracic portion. It is connected with the thoracic portion of the sympathetic trunk 

 by a slender intermediate portion of the trunk that may pass through the diaphragm 

 or behind it (fig. 719). The continuation of the lumbar into the sacral portion is also 

 slender, and descends behind the common iliac artery. The right trunk is partly 

 covered by the vena cava inferior and the left by the aorta. 



The ganglia, which are small and oval, vary in number from three to eight, but 

 are usually four. Rarely they are so fused as to form one continuous ganglion. 



White rami communicantes pass to the ganglia from the first two or three lum- 

 bar nerves only. This portion of the trunk also receives efferent splanchnic fibres 

 which are derived from the white rarni communicantes of the lower thoracic nerves 

 and continued downwards in the trunk. 



Branches. As in the thoracic region, the communicating branches are central 

 and peripheral. The central are grey rami communicantes. There may be two 

 branches to a nerve or one ramus may divide so as to join two adjacent spinal 

 nerves. Sometimes a spinal nerve may receive as many as five grey rami from the 

 sympathetic trunk. 



The peripheral branches include: (a) Branches passing to the aorta and taking 

 part in the formation of the aortic plexus; (b) branches which descend in front of the 

 common iliac artery to the hypogastric plexus; and (c) branches to the vertebra? and 

 ligaments. 



THE SACRAL PORTION OF THE SYMPATHETIC TRUNK 



The sacral part of each trunk passes downwards in front of the sacrum, imme- 

 diately outside the inner borders of the anterior sacral foramina. It is continu- 

 ous above with the lumbar portion of the trunk, and below it anastomoses freely in 

 front of the coccyx with the trunk of the other side to form a plexus in the terminus 

 of which is the coccygeal ganglion (ganglion coccygeum impar) (fig. 719). Like 

 the cervical and lower lumbar portions of the sympathetic trunk, the sacral part 

 receives no white rami communicantes from the spinal nerves. 



The sacral ganglia are small in size, and usually four in number. The variation 

 both in size and number is more marked in this portion of the trunk than in the 

 other two parts. 



Branches. The branches of the sacral ganglia include: 



(1) Grey rami communicantes to the sacral nerves. 



(2) Branches to the front of the sacrum which anastomose with their fellows of 

 the opposite side (commissural branches). 



(3) Branches which enter into the formation of the plexus on the middle sacral 

 artery. 



(4) Branches which join the pelvic plexuses. 



(5) Branches given off by the ganglion coccygeum impar to the coccyx and its 

 ligaments and to the glomus coccygeum (coccygeal gland). 



