THE TllOlt.Wic SYMPATHETIC 



sympathetic fibre.-.); (li) fibres which pass dorsalwards into the posterior primary 

 divisions of the nerves (!) lilircs which pass outwards in the anterior primary 

 divisions of the nerves. The last two groups of fibres are distributed to the blood- 

 vessels of the body-walls, to the skin-elands, and to the muscles of the hairs of the 



body. 



The peripheral branches form two series, an upper and a lower. 

 Those of the upper x< ;/< \ pass from the upper four or five ganglia ventralwards 

 and inwards to be distributed ae follows: 



(1) Pulmonary branches which accompany the intercostal arteries towards their 

 aortic origin without forming plexuses around them, and pass to the posterior pul- 

 monary plexus (fig. 720). 



(2) Aortic branches, some of which arise directly from the ganglia and some 

 from the pulmonary branches, and unite with branches from the cardiac plexus 

 and from the splanchnic nerves to surround the aorta as the thoracic aortic 

 plexus (fig. 720). This plexus accompanies the aorta into the abdomen and there 

 joins with the ccrliac (solar) plexus. 



(3) (Esophageal branches join with the oesophageal plexus of the vagus. 



(4) Vertebral branches, some of which pass with the nutrient arteries into the 

 bodies of the vertebra and some of which pass to the median line and there anastomose 

 with similar branches from the opposite side (commissural branches). 



The peripheral branches forming the lower series consist largely of efferent fibres 

 from the spinal nerves, which pass through the ganglia and reinforce the sympathetic 

 filaments proper. Thus composed, these branches run ventralwards and inwards on 

 the sides of the bodies of the vertebrae and unite to form the splanchnic nerves 

 which supply the abdominal organs. 



(1) The great splanchnic nerve may be formed by branches from all the 

 thoracic ganglia from the fifth to the tenth inclusive, or it may receive fibres from 

 only two or three of these ganglia (fig. 719). It is usually formed by branches from 

 the fifth to the tenth. The superior branch, usually the largest, receives smaller 

 inferior branches from the lower ganglia as it passes downwards on the sides of the 

 bodies of the vertebrae in the posterior mediastinum. The nerve enters the abdomi- 

 nal cavity by passing through the cms of the diaphragm, and joins the upper end of 

 the cceliac (semilunar) ganglion of the coeliac (solar) plexus. Near the bottom of the 

 eleventh or the top of the twelfth thoracic vertebra there is formed on the nerve 

 the splanchnic ganglion. Filaments from the nerve and from this ganglion pass 

 along the intercostal arteries to the aorta, oesophagus, and the thoracic duct, and 

 some fibres from the right side pass to the vena azygos (major). Sometimes this 

 nerve divides into two cords, giving off numerous branches which anastomose with 

 each other and with the small splanchnic nerve to form a plexus, in the meshes of 

 which are found some small ganglia. 



(2) The lesser splanchnic nerve receives fibres from the ninth and tenth 

 ganglia. Its course is similar to that of the great splanchnic nerve (fig. 719), but on 

 a posterior plane, and it terminates in the cceliac (solar) or renal plexuses. 



(3) The least splanchnic nerve, not always present, arises from the last thoracic 

 ganglion or sometimes from the small splanchnic nerve. It passes through the crus 

 of the diaphragm and ends in the renal plexus. 



Construction of the thoracic portion of the cord. The majority of the 

 sympathetic fibres which pass from the central nervous system enter the thoracic por- 

 tion of the sympathetic trunk ; some end there in ramifications around the cells of 

 its ganglia, while others merely pass through on their way to more distant termina- 

 tions. With regard to those which terminate in the ganglia, it has been shown that 

 in the dog and cat many end in the ganglion stellaturn, which corresponds with the 

 last cervical and the upper three or four thoracic ganglia in man. Among these are 

 the fibres conveying secretory impulses to the sweat-glands of the upper limb, 

 which emerge from the spinal cord in the thoracic nerves from the sixth to the 

 ninth, and, in the dog, vaso-constrictor fibres of the pulmonary blood-vessels which 

 leave the spinal cord in the second to the seventh thoracic nerves. Other fibres 

 which terminate' around the thoracic sympathetic ganglion-cells in the dog and cat 

 are the vaso-constrictor fibres for the upper limbs and some of the vaso-constrictor 

 fibres for the lower limbs. 



( )f the fibres which traverse the thoracic portion of the sympathetic trunk to gain 

 more distant terminations, some ascend to the cervical region (p. 1007), others descend 

 c,t 



