256 SPECIAL PHYSIOLOGY. 



centres; and, secondly, to connect many points of local distribution 

 with some given portion of the nervous centres. Thus, muscles sup- 

 plied through such a plexus, are brought into physiological relation 

 with various portions of the cord. In the same manner, nerve fibres 

 having different endowments, sensory, motor, or reflex, are hereby 

 intermixed; and, moreover, fibres possessing the same endowments, 

 are more widely distributed. 



The Sympathetic Nervous System. 



The sympathetic nervous system consists of two knotted yanglionated 

 nervous cords, which are placed one on each side of the vertebral 

 column, in the neck, in the thorax, in the abdomen, arid in the pelvis, 

 Fig. 62. These cords are connected with certain other ganglia situ- 

 ated deeply between the bones of the cranium and the face, and also 

 with certain important interlacements, or sympathetic plexuses, and 

 ganglia, placed on, or near, the great viscera in the chest and abdomen, 

 and named the prevertelral sympathetic plexuses. By many authori- 

 ties, the ganglia connected with the trunks or roots of certain cranial 

 nerves, and those situated upon the posterior roots of the spinal nerves, 

 are regarded as belonging to the sympathetic system. 



The ganglia of the sympathetic are fewest and largest in the neck, 

 there being only three, instead of a number equal to that of the cer- 

 vical nerves: perhaps a process of fusion here takes place. The supe- 

 rior cervical ganglion measures at least 1J inch in length ; there are 

 also a middle and lower cervical ganglion, the former being sometimes 

 absent. The dorsal ganglia are more regular, being usually twelve 

 in number, and of more moderate size. The lumbar and sacral ganglia 

 become still smaller, and lie in front of the bodies of the vertebrae, in- 

 stead of at the sides. Lastly, the ganglionated cords of the two sides, 

 terminate below in a single coccygeal ganglion, placed on the front of 

 the coccyx. Each of these ganglia, from the neck to the pelvis, is 

 connected with the adjacent spinal nerve, as those in the cranium and 

 face are with the cranial nerves, by one, or generally two, short ner- 

 vous cords proceeding outwards; besides this, each is, of course, con- 

 nected with the ganglia above and below it, by the main trunk of the 

 sympathetic itself; finally, each gives off a branch inwards to the so- 

 called prevertebral plexuses. 



From the superior cervical ganglion of the sympathetic, branches 

 ascend to the base of the skull, and form direct, or indirect, communi- 

 cations with certain cranial nerves ; as, for example, with the third, 

 sixth, facial or portio dura of the seventh, and particularly with the 

 fifth nerves. It is with these branches, also, that the small sympa- 

 thetic ganglia, found in the spaces between the cranial and facial bones, 

 are connected, viz., the lenticular ganglion in the orbit, the otic gan- 

 glion and the spheno -palatine ganglion behind the nasal cavities, and 

 the submaxillary ganglion situated on the submaxillary salivary gland; 

 all four ganglia are connected with branches of the fifth cranial nerve. 



Of the prevertebral plexuses of the sympathetic, the chief are the 

 cardiac, the solar, and the hypogastric; but there are several secondary 



