SPLANCHNIC NERVES 831 



upper ten ganglia lie upon the heads of the corresponding ril)S, ininiediatdy under 

 cover of the jdeura. The lower two are i)laced further forwards, and lie on the 

 sides of the bodies of the eleventh and twelfth thoracic vertebra? between the bones 

 and the diaphragm. The cord is continuous above with the cervical part of the 

 cord, the first thoracic ganglion being sometimes united across the neck of the first 

 rib with the inferior cervical ganglion. Below, the cord enters the abdominal 

 cavity In- i»assing lx4nnd the ligamentum arcuatum internum to become continuous 

 with the lunil)ar part of the cord. The first thoracic ganglion (ganglion stella- 

 tum) is larger than the others, and is of an irregular form. The remainder of the 

 series are triangular in outline, two of the angles being continued into the inter- 

 ganglionic part of the cord, and the other into the rami communicantes. On some 

 of the loAver ganglia a fourth angle makes its appearance, and is continued into one 

 of the roots of the splanchnic nerves. 



Branches, — The l^ranches are classified into external and internal. The 

 external branches are the rami communicantes. A grey and a white ramus 

 (.•onnnunicans connects each ganglion with the corresponding thoracic nerve. The 

 internal branches are the rand efferentcs, those of the upper four ganglia are 

 distriluited chiefiy to the aorta and lungs. The internal branches of the lower 

 eight ganglia form three splanchnic nerves which are distributed to tlie alidominal 

 viscera. 



Internal branches. — Upper series. — From the upper four or five ganglia fine 

 twigs arise Avhich are distributed to the thoracic aorta, mediastinum, lungs, verte- 

 brae, and ligaments. 



Internal branches, — Lower series. — These branches, although arising in the 

 thorax, are destined for the abdominal viscera. The branches from the fifth to the 

 ninth ganglia unite to form the great splanchnic nerve; the lesser splanchnic nerve 

 arises by two roots from the tenth and eleventh ganglia, while the internal Ijranch 

 of the twelfth ganglion forms the smallest splanchnic nerve. 



GREAT SPLANCHNIC NERVE. — The five roots of this nerve run downwards 

 and inwards, Ix'tween the ])L'ura and the bodies of the thoracic vertebrae, and unite 

 within the posterior mediastinum to form a trunk of considerable size. The nerve 

 thus fomied pierces the crus of the diaphragm, and enters the semilunar ganglion 

 of its own side. 



The great splanchnic nen'e is whitish in colour, owing to a number of luedullated fibres 

 iitering into its composition. Occasionally a small ganglion (splanchnic ganglion) is developed 

 upon it in the mediastinum. This ganglion is constant on the right side. (Cunningham.) 



The LESSER SPLANCHNIC NERVE runs a shnilar course to the great splanch- 

 nic, but at a lower le-vel. It ]>ierees the crus of the diapln-agm, or passes 

 through the internal arcuate ligament, and enters the solar and renal plexuses. 



The SMALLEST SPLANCHNIC NERVE passes behind the internal arcuate liga- 

 ment or through the crus of the diaphragm and enters the renal plexus. 



The majority of the sympathetic fibres which pass from the central nervous 

 system enter the dorsal part of the sympathetic chain; some end there, in ramifi- 

 cations around the cells of the ganglia, and others merely pass through on their 

 way to more distant terminations. V\ ith regard to those which terminate in the 

 ganglia it has been shown that in the dog and cat many end in the ganglion stel- 

 latum. which corresponds with the last cer\'ical and the upper three or four dorsal 

 ganglia in man: amongst these are the secretory fibres to the sweat glands of the 

 U))per limb which emerge from the spinal cord by the dorsal nerves from the sixth 

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

 which leave the spinal cord by the second to the seventh dorsal nerves. Other 

 fibres which terminate around the thoracic ganglion cells in the dog and the cat are 

 the vaso-con.strictor fibres of the upper limbs and some of the vaso-constrictor fibres 

 of the lower liml). 



Of the fibres which traverse the dorsal part of the sympathetic cord, to gain 

 more distant terminations, some ascend to the cervical region (p. 830), others 

 descend to the lumbar region, and many pass by the rami efferentes to the splanch- 

 nic nerves. 



Amongst those which descend to the lumbar region are pilo-motor fibres, vaso- 



