1040 THE NERVOUS SYSTEM 



THE SACRAL PORTION OF THE SYMPATHETIC TRUNK 



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

 diately lateral to the medial borders of the anterior sacral foramina. It is 

 continuous 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. 787). 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 varia- 

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

 the two parts above. 



Branches. — The branches of the sacral gangha include : — 



(1) Grej' 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 ganghon coccygeum impar to the coccyx and its ligaments 

 and to the glomus coccygeum (coccygeal gland). 



Construction of the lumbar and sacral portions of the gangliated trunk. — The gangha 

 of both these portions of the tnmk are very variable in shape, size, position, and number. There 

 are usually four gangha belonging to each portion, but sometimes as many as eight may be 

 distinguished in the lumbar and at other times there may be as many as six in the sacral portion. 

 In the majority of cases, especially in the sacral region, these masses of cells are so fused that 

 their number is less than the number of the spinal nerves with which they are associated. As 

 noted above, only the first two or three lumbar spinal nerves send white rami which enter these 

 ganglia directly as such. However, visceral efferent fibres descend this entire stretch of the 

 trunk, through both the lumbar and sacral portions, from the white rami of the lower thoracic 

 and the upper lumbar nerves above. These fibres either terminate in the various ganglia or 

 pass uninterrupted to the more distant sympathetic cell-bodies which are concerned in impulses 

 that are vaso-motor to the genital organs, motor for the uterus, the vas deferens, and the mus- 

 cular coats (circular coat especially) of the bladder. Also, some of them convey secretory, pilo- 

 motor, and vaso-motor impulses for the glands, skin, and vessels of the lower extremity in 

 addition to the similar impulses conveyed in the peripheral branches from the lower part of 

 the thoracic portion of the sympathetic trunk. The motor impulses for the uterus or vas 

 deferens and for the bladder pass, in most part probably, by way of the peripheral branches 

 from the lumbar portion of the cord, through the aortic plexus to the inferior mesenteric gang- 

 lion; others, the vaso-motor impulses to the genital organs especially, pass by way of the sacral 

 ganglia and the peripheral branches from them to the hypogastric or pelvic plexus and the appro- 

 priate subplexuses of this region. Of the vaso-motor fibres for the penis, some of the constrictor 

 fibres pass down the sacral portion of the sympathetic trunk and terminate about the cells of 

 the sacral ganglia, and these cells send out sympathetic fibres which join and course in the pudic 

 nerve (n. pudendus). 



All of both the lumbar and sacral spinal nerves receive grey rami from the gangliated trunk. 

 These, just as those from the other portions of the trunk, consist of — (1) vaso-motor fibres to 

 vessels of the meninges and the vertebral canal; (2) sympathetic fibres which join the divisions 

 of the spinal nerves and course in them to their distribution, and (3) afferent sympathetic 

 fibres terminating in the spinal ganglia. 



In addition to the visceral efferent fibres, the branches of the lumbo-sacral portion of the 

 sympath(!tic trunk carry cerebro-spinal fibres of general sensibility — sensory fibres arising in 

 the spinal ganglia of this and the lower thoracic region. 



There are no white rami proper passing from the sacral spinal nerves to course or terminate 

 in the sympathetic trunk. Visceral efferent fibres are given off by these nerves in abundance, 

 but, instead of entering the trunk and its ganglia, they form bundles which pass over the trunk 

 and (lircictly into its peripheral branches and to the more distant ganglia. The bundles passing 

 from tlie second, third, and fourth sacral nerves are large and especially definite. While 

 homologous to wliite ntiiii, such bundles are better known as tlie visceral branches of the sacral 

 nerves or the plevic splanchnics. They contain some spinal sensory fibres, but consist for the 

 most part of visceral effereiit, conveying impulses, vaso-motor (vaso-dilator, chiefly) to the gen- 

 ital organs, both motor and inhibitory for the rectum, uterus, and bladder (longitudinal coat 

 especially), and secretory for the prostate gland. Tiiese fibres contribute to the hypogastric 

 plexus and are interrupted in the small ganglia of its sub-plexuses, named according to the 

 various urino-genital organs concerned. 



THE GREAT PREVERTEBRAL PLEXUSES 



The great prevertebral plexuses, in the body cavities, are three in number — 

 the cardiac, the cfX'liac (solar or epigastric), and the hypogastric or pelvic. The 

 cardiac plexus lies boiiind and below the arch of the "aorta, and the cocliac and 



I 



