1364 HUMAN ANATOMY. 



the subclavain artery, inosculates with the middle cervical cardiac and inferior laryngeal 

 nerves and terminates in the deep cardiac plexus. 



THE THORACIC PORTION OF THE GANGLIATED CORD. 



The thoracic portion of the gangliated cord (pars thoracalis systematis sympa- 

 thetici) consists of a series of eleven, twelve, ten or even fewer irregularly triangular, 

 fusiform or oval ganglia (gg. thoracalia), situated lateral to the bodies of the thoracic 

 vertebrae, covered by parietal pleura and interconnected by association cords which 

 lie anterior to the intercostal blood-vessels (Fig. 1133). The largest of the ganglia 

 is the first, which is situated at the mesial end of the first intercostal space and is 

 not infrequently fused with the inferior cervical ganglion. The location of the 

 thoracic ganglia corresponds usually to the heads of the ribs, the lowest being placed 

 anterior to the head of the twelfth rib and at the upper margin of the twelfth thoracic 

 vertebra. 



A characteristic of the thoracic ganglia is the almost unvarying presence of white 

 rami communicantes ', all of the series, with the possible exception of the first, receiving 

 these rami from the thoracic spinal nerves. They consist of an zipper and a lower 

 series, the former coming from the upper five nerves and coursing head-ward to enter 

 and be distributed mainly by way of the cervico-cephalic portion of the gangliated 

 cord ; and the lower arising from the lower seven and being distributed to certain 

 thoracic and abdominal structures. As elsewhere, so here from each of the ganglia 

 is given off a gray ramus communicans to a thoracic spinal nerve. 



The somatic branches of the thoracic portion of the gangliated cord are 

 chiefly the gray rami communicantes. These arise from each of the thoracic ganglia 

 and, in close proximity to the white rami, pass backward and join the anterior pri- 

 mary divisions of all the thoracic spinal nerves. 



The visceral branches arise from the ganglia and their association cords and 

 consist of gray splanchnic efferent and white splanchnic efferent and afferent fibres. 



The splanchnic afferent fibres have no sympathetic connections, and consist 

 merely of tracts which carry impulses from the splanchnic area through the thoracic 

 and spinal ganglia to the posterior roots of the spinal thoracic nerves. 



The splanchnic efferent fibres, after passing through the gangliated cord or 

 its peripheral branches, form links with the cells of the collateral or terminal ganglia, 

 from which nonmedullated axones are derived for the supply of various visceral or 

 vascular structures. Those of the upper series are distributed mainly as branches of 

 the cervical ganglia; while those of the lower series, from the sixth to the twelfth thoracic 

 nerves inclusive, in the thorax supply the aorta and lungs with vasomotor fibres. 

 Below the thorax their distribution is quite extensive, including, in conjunction with 

 the vagus, viscero-inhibitory fibres for the stomach and intestine, motor fibres for a 

 portion of the circular muscle of the rectum, vasomotor fibres for the abdominal aorta 

 and its branches and secretory and sensory fibres for the abdominal viscera. The 

 thoracic gangliated cord is peculiar in containing, along with the visceral fibres dis- 

 tributed by its splanchnic efferents, many efferents proceeding from the spinal cord 

 destined for regions supplied by way of the limb nerves arising from the cervical and 

 lumbo-sacral segments of the spinal cord. In order to provide gray rami at appro- 

 priate levels to join the spinal nerves the spinal efferents course both up and down 

 in the gangliated cord beyond the thoracic region. In this manner the thoracic 

 nerves, in addition to giving off the splanchnic efferents, provide vasomotor, pilo- 

 motor and secretory filaments for the greater part of the lower half of the body. 



The visceral branches comprise : (i) the pulmonary branches, (2) the aortic 

 branches and (3) the splanchnic nerves. 



1. The pulmonary branches (IT. pulmoualcs) are derived from the second, 

 third and fourth ganglia and proceed forward to join the posterior pulmonary plexus. 



2. The aortic branches arise from the upper four or five ganglia and, after 

 furnishing a few fine tui^s to the vertebras and their ligaments, inosculate around 

 the thoracic aorta in the form of a fine plexus (plexus anrtictis thoracalis). 



3. The splanchnic nerves (nn. splanchnici) (Fig. 1133) are three trunks 

 which arise from the lower part of the; thoracic cord and are distributed to structures 

 situated in the abdominal cavitv. 



