THE AUTONOMIC NERVE SYSTEM 659 



THE PHYSIOLOGIC ANATOMY OF THE AUTONOMIC NERVE SYSTEM 



In a consideration of the essential facts of the physiologic anatomy of 

 this system, it will be found convenient to consider first the sympathetic 

 ganglia, and the distribution of their post-ganglionic fibers. 



The Sympathetic Ganglia. The sympathetic ganglia may for con- 

 venience of description be divided into three groups: viz., the vertebral or 

 lateral, the pre-vertebral or collateral, and the peripheral or terminal. 



The vertebral ganglia are arranged in the form of chains, one on each 

 side of the vertebral column. The number of ganglia in the chain varies in 

 animals of different and in animals of the same species. In man the number 

 varies from 20 to 22. Each chain may be divided into a cervical, a thoracic 

 a lumbar, a sacral, and a coccygeal portion. The cervical portion is usually 

 described as consisting of three ganglia a superior, a middle and an inferior. 

 This statement is open to question, however, as the middle one is frequently 

 absent and the inferior is regarded by some anatomists as belonging to the 

 pre-vertebral series. The thoracic portion consists of ten or twelve ganglia, 

 the lumbar and sacral portions of four each and the coccygeal portion of one, 

 the so-called ganglion impar. 



The pre-vertebral ganglia are also united in the form of a chain situated 

 in the abdominal cavity. The ganglia constituting this chain are known as 

 the semilunar, the renal, the superior and inferior mesenteric, and hypogas- 

 tric, or pelvic. 



The peripheral ganglia are in more or less close relation with tissues and 

 organs in different regions of the body. Among the members of this group 

 may be mentioned the ciliary or ophthalmic, the spheno-palatine, the otic 

 and the submaxitlary ganglia; the ganglia in the walls of the heart, in the 

 walls of the respiratory organs, in the walls of the stomach, intestines and 

 at the base of the bladder (the pelvic ganglia). 



Structure of the Ganglia. Each ganglion consists of a capsule or 

 stroma of connective tissue, in which are contained large numbers of nerve- 

 cells, nerve-fibers, medullated and non-medullated, and blood-vessels. The 

 nerve-cells give origin to two or more dendrites, which, perforating a nucle- 

 ated capsule by which each cell is surrounded, branch and re-branch and 

 interlace to form a pericapsular plexus. Each cell gives origin to an axon, 

 which as it leaves the cell becomes invested with a sheath continuous with 

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

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

 in its entirety, is known as a sympathetic neuron. The axonic processes as 

 they emerge from the cells become united and in many instances form dis- 

 tinct nerve strands, but subsequently as they approach their distribution 

 divide and subdivide, forming smaller and even smaller bundles, which pass 

 in different directions to regions varying in position according to the situa- 

 tion of the ganglion from which they come. These post-ganglionic fibers 

 are for descriptive purposes divided into two groups, viz. : (i) the gray rami 

 communicantes, and (2) the rami viscerales. 



THE ANATOMIC RELATIONS OF THE SYMPATHETIC GANGLIA 

 TO PERIPHERAL STRUCTURES 



The Vertebral Ganglia. i. The gray rami communicantes. The fibers 

 composing these branches, as the name implies, communicate with the 



