ABDOMINAL PAET OF THE SYMPATHETIC SYSTEM. 761 



The peripheral branches supplying thoracic organs contain vaso-motor fibres 

 for the lungs and aorta.' The peripheral branches from the lower part of the 

 sympathetic trunk in the thorax, receiving white rami from the lower thoracic 

 nerves, are distributed mainly to structures below the diaphragm. They comprise 

 (a) viscero-inhibitory fibres for the stomach and intestines ; (b) motor fibres for 

 part of the rectum ; (c) pilo-motor fibres for the lower part of the body ; (d) vaso- 

 motor fibres for the abdominal aorta and its branches, and for the lower limbs ; 

 (e) secretory, and (/) sensory fibres for the abdominal viscera. 



The branches from the gangliated trunk are, as in the neck, divisible into two 

 sets (A) Central branches, communicating with other nerves, and (2?) peripheral 

 branches, distributed in a plexiform manner to the thoracic and abdominal viscera. 



(A) Central Communicating Branches. The white rami communicantes from 

 the thoracic nerves have already been described. Passing forwards from the 

 anterior rami of the nerves, they become connected with the ganglia or the con- 

 necting cord of the sympathetic. 



The gray rami communicantes are branches arising irregularly from each thoracic 

 ganglion ; passing backwards along with the white rami, they join the anterior 

 rami of the thoracic nerves, and are distributed in a manner already described 

 (p. 754). 



(B) Peripheral Branches of Distribution. These branches arise irregularly 

 from the ganglia and the connecting cord. They are composed of non-medullated 

 (splanchnic efferent) fibres derived from the ganglion cells, and medulla ted fibres 

 (splanchnic efferent and afferent) derived directly from the white rami, without 

 the intervention of the cells of the ganglia. 



1. Rami Pulmonales. Pulmonary Branches. From the gangliated trunk 

 opposite the second, third, and fourth ganglia fine filaments arise which join the 

 posterior pulmonary plexus. 



2. Rami Aortici. Aortic Branches. The upper part of the thoracic aorta 

 receives fine branches from the upper five thoracic ganglia. 



3. Nn. Splanchnici. Splanchnic Nerves. Three nerves arise from the inferior 

 part of the gangliated trunk, partly from the ganglia themselves, and partly from 

 the connecting cord between the ganglia. Passing downwards over the bodies 

 of the thoracic vertebrae they pierce the diaphragm, to end in the abdomen. 



(a) N. Splanchnicus Major. The greater splanchnic nerve arises from the gangli- 

 ated trunk between the fifth and ninth ganglia. By the union of several irregular 

 strands a nerve of considerable size is formed, which descends in the posterior 

 mediastinum, and piercing the crus of the diaphragm, joins at once the anterior 

 end of the cceliac ganglion. In its course in the thorax the splanchnic ganglion 

 is formed upon the nerve. It is more prominent in the foetus than in the adult. 

 From both nerve and ganglion branches arise in the thorax, for the supply of 

 the oesophagus and descending thoracic aorta (Fig. 638). 



(6) N. Splanchnicus Minor. The lesser splanchnic nerve arises from the gangli- 

 ated trunk opposite to the ninth and tenth ganglia. It passes over the bodies of 

 the lower thoracic vertebrae, pierces the diaphragm near or along with the greater 

 splanchnic nerve, and ends in the coeliac plexus (aortico-renal ganglion). 



(c) N. Splanchnicus Imus. The lowest splanchnic nerve arises from the 

 last thoracic ganglion of the sympathetic, or it may be a branch of the lesser 

 )lanchnic nerve. It pierces the diaphragm, and ends in the renal plexus. 



III. PAES ABDOMINALIS SYSTEMATIS SYMPATHICI. 



The abdominal part of the sympathetic trunk is placed upon the bodies of 

 the lumbar vertebrae, medial to the origins of the psoas major muscle, and in front 

 of the lumbar vessels. It is connected with the thoracic portion of the trunk by 

 an attenuated cord which either pierces or passes behind the diaphragm. It is 

 continuous below with the pelvic portion of the trunk by means of a connecting cord, 

 which passes behind the common iliac artery. 



It is joined by medullated fibres (white rami communicantes) from the first two 



