THE SYMPATHETIC NERVE SYSTEM. 563 



the cell becomes invested with a sheath continuous with the capsule 

 surrounding the cell-body. It is, however, wanting in a medullary 

 sheath, and hence the nerve presents a gray color. Such a structure, 

 in its entirety, is known as a sympathetic neuron. 



Structure of the Interconnecting Cords. The interconnecting 

 cords are composed of non-medullated and medullated nerve-fibers. 

 The former are the axons of cells found in the ganglia more centrally 

 located ; the latter, as will be stated later, are derived from the spinal 

 nerves, from the fibers of which, however, they differ in character, 

 being much smaller and finer. The fibers of the interconnecting 

 cords, as a rule, transmit nerve impulses from the more centrally to 

 the more peripherally located ganglia, and are therefore termed 

 rami efferentes. In the vertebral chain some of the cords transmit 

 nerve impulses upward, others downward, others again forward, to 

 the pre- vertebral and peripheral ganglia. 



Among the rami efferentes, interconnecting cords, there are some 

 which possess special interest for the physiologist, viz. : 



1 . The cervical, which connects the thoracic ganglia with the superior 



cervical ganglion. It is composed mainly of medullated nerve- 

 fibers which are derived originally from the spinal nerves. 



2. The great splanchnic nerve, formed by the union of branches from 



the fifth to the tenth thoracic ganglia. It connects these ganglia 

 with the semilunar ganglion. 



3. The small splanchnic nerve, formed by the union of branches from 



the ninth and tenth thoracic ganglia. It connects these ganglia 



with the solar and renal plexuses. 



Distribution of the Sympathetic Fibers. It has been demon- 

 strated by histologic and physiologic methods of investigation that 

 the sympathetic non-medullated fibers which have their origin in 



receiving a motor filament from the motor oculi communis and a sensory filament 

 from the nasal branch of the fifth. 12. Spheno-palatine ganglion. 13. Otic gang- 

 lion. 14. Lingual branch of the fifth nerve. 15. Submaxillary ganglion. 16, 

 17. Superior laryngeal nerve. 18. External laryngeal nerve. 19, 20. Recurrent 

 laryngeal nerve. 21, 22, 23. Anterior branches of the upper four cervical nerves, 

 sending filaments to the superior cervical sympathetic ganglion. 24. Anterior 

 branches of the fifth and sixth cervical nerve, sending filaments to the middle 

 cervical ganglion. 25, 26. Anterior branches of the seventh and eighth cervical 

 and the first dorsal nerves, sending filaments to the inferior cervical ganglion. 

 27. Middle cervical ganglion. 28. Cord connecting the two ganglia. 29. In- 

 ferior cervical ganglion. 30, 31. Filaments connecting this with the middle 

 ganglion. 32. Superior cardiac nerve. 33. Middle cardiac nerve. 34. Inferior 

 cardiac nerve. 35,35. Cardiac plexus. 36. Ganglion of the cardiac plexus. 37. 

 Nerve following the right coronary artery. 38, 38. Intercostal nerves, with their 

 two filaments of communication with the thoracic ganglia. 39, 40, 41. Great 

 splanchnic nerve. 42. Lesser splanchnic nerve. 43, 43. Solar plexus. 44. Left 

 pneumogastric. 45. Right pneumogastric. 46. Lower end of the phrenic nerve. 

 47. Section of the right bronchus. 48. Arch of the aorta. 49. Right auricle. 

 50. Right ventricle. 51,52. Pulmonary artery. 53. Right half of the stomach. 

 54. Section of the diaphragm. (Sappey.} 



