6lO NERVOUS SYSTEM 



together by the so-called sympathetic cord. They have a number of 

 filaments of communication above with the cranial and the cervical 

 nerves of the cerebro-spinal system. Branches from the superior 

 ganglion go to the internal carotid to form the carotid and the cavern- 

 ous plexuses, following the vessels as they branch to their distribution. 

 Branches from this ganglion pass to the cranial ganglia. There also 

 are branches that unite with filaments from the pneumogastric and the 

 glosso-pharyngeal to form the pharyngeal plexus, and branches that 

 form a plexus on the external carotid, the vertebral and the thyroid 

 arteries, following the ramifications of these vessels. 



From the cervical portion of the sympathetic, the three cardiac 

 nerves arise and pass to the heart, entering into the formation of the 

 cardiac plexus. The superior cardiac nerve arises from the superior 

 ganglion ; the middle nerve, the largest of the three, arises from the 

 middle ganglion, or from the sympathetic cord when this ganglion is 

 wanting ; and the inferior nerve arises from the inferior cervical ganglion 

 or the first thoracic. These nerves present frequent communications 

 with various of the adjacent cerebro-spinal nerves, penetrate the tho- 

 rax and form the deep and superficial cardiac plexuses and the pos- 

 terior and the anterior coronary plexuses. In these plexuses there are 

 found ganglioform enlargements ; and on the surface and in the sub- 

 stance of the heart, are collections of nerve-cells connected with the 

 fibres. 



Thoracic Ganglia. The thoracic ganglia are situated in the chest, 

 beneath the pleura, and rest on the heads of the ribs. They usually 

 are twelve in number, but occasionally two are fused into one. They 

 are connected together by the sympathetic cord. They each communi- 

 cate by two filaments with the cerebro-spinal nerves. One of these is 

 white, like the spinal nerves, and probably passes to the sympathetic, 

 and the other, of a grayish color, is thought to contain the true sympa- 

 thetic filaments. From the upper six ganglia filaments pass to the aorta 

 and its branches. The branches that 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, receiv- 

 ing a few filaments from the upper six ganglia. This is a large, white, 

 rounded cord, which penetrates the diaphragm and passes to the semi- 

 lunar ganglion, sending 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 frequent anastomoses with each other. 



