CCELIAC PLEXUS. 763 



This portion of the sympathetic trunk is placed on the pelvic surface of the 

 sacrum, medial to the anterior sacral foramina. It is connected above by a 

 cord with the abdominal portion of the sympathetic, and below it ends in 

 a plexiform union over the coccyx with the trunk of the other side, the two 

 being frequently connected by the ganglion impar or coccygeal ganglion. The 

 number of ganglia is variable ; there are commonly four. They are of small size, 

 gradually diminishing from above downwards. 



Central communicating branches arise irregularly in the form of gray rami 

 communicantes from the sacral ganglia, which join the anterior rami of the sacral 

 and coccygeal nerves. 



Peripheral Branches of Distribution. (1) Visceral branches of small size arise 

 from the upper part of the pelvic sympathetic trunk, and join the pelvic plexus 

 (see below). 



(2) Parietal branches, also of small size, ramify over the front of the sacrum, and 

 form, in relation to the middle sacral artery, a plexiform union with branches from 

 the sympathetic trunk of the other side. 



PLEXUS SYMPATHICI. 



Sympathetic Plexuses. It has already been seen that the peripheral branches 

 the sympathetic trunk, throughout its length, are characterised by forming or 

 joining plexuses in their neighbourhood. 



The cervical sympathetic ganglia and nerves give rise to the carotid and 

 cavernous plexuses ; the external carotid, pharyngeal, thyreoid, vertebral, and 

 subclavian plexuses; and they send important branches to the cardiac plexuses 

 (described with the vagus nerve). 



The thoracic ganglia send branches to join the pulmonary and cesophageal 

 plexuses (described with the vagus nerve). They form plexuses on the thoracic 

 aorta, and by means of the splanchnic nerves they form the chief source of 

 the coeliac plexus. 



THE CCELIAC AND PELVIC PLEXUSES. 



These great plexuses serve to distribute nerves to the viscera and vessels of the 

 abdominal and pelvic cavities. Taken together they include three plexuses the 

 coeliac plexus, the hypogastric plexus, and the pelvic plexus. They are constituted 

 by peripheral branches of the lower thoracic, abdominal, and upper pelvic parts 

 of the sympathetic trunk ; and they are related to the central nervous system 

 by means of the visceral branches (white rami communicantes) of the lower 

 thoracic and upper lumbar nerves on the one hand, and by the visceral branches 

 of the second and third, or third and fourth sacral nerves, on the other hand. The 

 thoracico-lumbar series join the sympathetic trunk, and reach the coeliac plexus 

 mainly through the splanchnic nerves, and to a lesser extent through the abdominal 

 part of the sympathetic trunk. The sacral series enter the pelvic plexus without 

 connexion with the sympathetic trunk. The hypogastric plexus serves as a con- 

 necting link between the coeliac and pelvic plexuses. 



PLEXUS CCELIACUS. 



The coeliac plexus lies on the posterior abdominal wall in relation to the 

 abdominal aorta and behind the stomach. It is composed of three elements : the 

 coeliac plexus surrounding the origin of the coeliac artery, between the crura of 

 the diaphragm ; and two cceliac ganglia, each lying on the corresponding or us of 

 the diaphragm, and overlapped by the suprarenal gland, and on the right side 

 by the inferior vena cava. The plexus is continuous with subordinate plexuses, 

 diaphragmatic, suprarenal, renal, superior mesenteric and aortic; and by means 

 of the hypogastric nerves the aortic plexus is continued into the hypogastric 

 plexus, which again forms the chief origin of the pelvic plexuses. 



The coeliac ganglia constitute the chief ganglionic centres in the cceliac 

 plexus. They are irregular in form. They are often partially subdivided, and one 



