THE SYMPATHETIC NERVOUS SYSTEM 711 



spinal nerves, through which they are distributed to the unstriped muscuhir tissue and ghxnds, 

 as vasomotor, pilomotor, and secretory nerves. The sympathetic, like the cerebrospinal system, 

 consists of neurones, each of which comprises the cell-body, an axone, and numerous branched 

 dendrites. The (■cil-h()di(>s arc aggrefjated into ganglia, some of wliich are large and more or 

 less constant in position and form, while others are microscopic and are scattered in an irregular 

 manner through tiie peripheral part of the system. It is prol)al)le that simple visceral reflexes 

 may be mediated by sympathetic; neurones alone. 



In descriptive anatomy the sympathetic system is regarded as consisting of 

 (1) a chain of ganglia extending along either side of the vertebral column and con- 

 nected by association fibers to form the sympathetic trunk; (2) central branches 

 to and from the cerebrospinal nerves; (3) peripheral branches, which form plexuses 

 with each other and the cerebrospinal nerves; (4) the peripheral ganglia which are 

 interposed in the plexuses. 



The sympathetic trunk (Truncus sympathicus) extends on either side from 

 the base of the cranium to the tail. In it are interposed, at intervals of varying 

 regularity, the ganglia of the sympathetic trunk (Ganglia trunci sympathici). 

 These are connected with the cerebrospinal nerves by central branches, the rami 

 communicantes. 



Two kinds of rami communicantes occur. Of these, one type consists largely of medullated 

 fibers derivetl from the spinal nerves and ganglia; they have therefore a white appearance, and 

 are termed white rami. They contain both efferent and afferent fibers. The efferent splanch- 

 nic fibers are deri\'ed from the ventral roots of the spinal nerves and terminate in great part 

 about the cells of the nearest sympathetic ganglion; others end in more distant or in periph- 

 eral ganglia. The afferent splanchnic fibers are chiefly peripheral processes of the cells of the 

 spinal ganglia, but some are .sympathetic fll)ers which enter the spinal nerve-trunk and terminate 

 at)OUt cells of the spinal ganglion. The gray rami consist mainly of non-medullated fibers derived 

 from the sympathetic ganglia directly or through tlie trunk, which proceed centrally to the 

 spinal nerves and are distributed along the somatic divisions of the latter to unstriped muscle and 

 glands as vasomotor, pilomotor, and secretory fibers. Some go to the membranes of the spinal 

 cord, and a few terminate about cells of the spinal gangha as sensory sympathetic fibers. 



Similar but more complex and irregular communications which exist between 

 the sympathetic system and the cranial nerves — with the exception of the first 

 and second — have been referred to in the accounts of the latter. 



It is convenient for descriptive purposes to divide the sympathetic system into 

 cephalic, cervical, thoracic, abdominal, and pelvic parts. 



1. The cephalic part (Pars cephalica systematis sympathici) comprises the 

 otic, sphenopalatine, and ciliary gangha, which may be regarded as homologues of 

 the ganglia of the trunk of other regions. It also includes three plexuses formed by 

 branches derived from the superior cervical ganglion. The ganglion gives off two 

 or three filaments which subdivide to form the internal carotid plexus around the 

 artery of like name. The cavernous plexus stn-rounds the artery within the caver- 

 nous sinus and communicates with that of the o})posite side. The external carotid 

 plexus is formed around the homonymous artery, and filaments from it go to the 

 vessel and its branches and to the salivary glands. 



2. The cervical part (Pars cervicalis s. sympathici) includes two ganglia and 

 the trunk which connects them. 



The superior or anterior cervical ganglion (G. cervicale craniale) lies on the 

 guttural pouch below the occipito-atlantal articulation (Fig. 437). It is reddish- 

 gray in color, fusiform, and about an inch (ca. 2 to 3 cm.) in length. It is connected 

 by rami communicantes with the last four cranial and first cervical nerves, sends 

 branches to form the plexuses mentioned above, and contributes to the pharyngeal 

 plexus. 



The cervical trunk of the sympathetic connects the superior and inferior 

 cervical ganglia. On leaving the former it is associated in a common sheath with 

 the vagus along the dorsal face of the common carotid artery. At the root of the 

 neck it separates from the vagus and joins the inferior ganglion. 



The inferior or posterior cervical ganglion (G. cervicale caudale) is situated 

 under the first rib and the insertion of the scalenus (Figs. 428, 429). On the right 



