422 NEKVOTJS SYSTEM. 



enlargements ; and upon the surface and in the substance 

 of the heart, are numerous collections of nerve-cells con- 

 nected with the fibres, which were first accurately described 

 and figured by Dr. Robert Lee. 1 



Thoracic Ganglia. The thoracic ganglia are situated in 

 the chest, under the pleura, and rest on the heads of the 

 ribs. They are usually twelve in number, but occasionally 

 two are fused into one. They are connected together by 

 the sympathetic cord. They each communicate by two fila- 

 ments with the cerebro-spinal nerves ; one of these being 

 white, like the spinal nerves, and probably passing to the 

 sympathetic, and the other, of a grayish color, is thought to 

 contain the true sympathetic filaments. From the upper six 

 ganglia, filaments pass to the aorta and its branches. The 

 branches which form the posterior pulmonary plexus arise 

 from the third and fourth ganglia. The great splanchnic 

 nerve arises mainly from the seventh, eighth, and ninth 

 ganglia, receiving a few filaments from the upper six gan- 

 glia. This is a large, white, rounded cord, which penetrates 

 the diaphragm and passes to the semilunar ganglion, send- 

 ing a few filaments to the renal plexus and the suprarenal 

 capsules. The lesser splanchnic nerve arises from the tenth 

 and eleventh ganglia, passes into the abdomen, and joins the 

 coeliac plexus. The renal splanchnic nerve arises from the 

 last thoracic ganglion, and passes to the renal plexus. The 

 three splanchnic nerves present numerous anastomoses with 

 each other. 



Ganglia in the Abdominal and the Pelvic Cavity. 

 The semilunar ganglia on the two sides send off radiating 

 branches to form the solar plexus. They are situated by 

 the side of the coeliac axis and near the suprarenal cap- 

 sules. These are the largest of the sympathetic ganglia. 

 From these arise numerous plexuses distributed to various 



1 LEE, On the Ganglia and Nerves of the Heart. Philosophical Transactions, 

 1849, Part i., London, 1849. 



