the sympathetic nervous system 829 



Coccygeal Nerves 

 The coccygeal nerves (Nn. coccygei) commonly number five pairs. Their 

 dorsal and ventral branches anastomose to form respectively two trunks on either 

 side, which extend to the tip of the tail and supply its muscular and cutaneous 

 nerves. The dorsal trunk runs with the dorso-lateral artery between the sacro- 

 coccygeus dorsalis and intertransversales muscles (Fig. 579). The ventral trunk 

 accompanies the ventro-lateral artery below the intertransversales. 



The Sympathetic Nervous System ^ 



The S3niipathetic nervous system (Systema nervorum sympathicum) is that 

 part of the nervous system which serves (1) to transmit stimuli to the heart muscle, 

 unstriped muscle, and glands; (2) to conduct impulses from the viscera to the cere- 

 brospinal system. 



. Many of the fibers are derived from the cerebrospinal system and are rearranged and dis- 

 tributed m the sympathetic system. Numerous sympathetic fibers are contributed to the cerebro- 

 spmal nerves, through which they are distributed to the unstriped muscular tissue and glands, 

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

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

 dendrites. The cell-bodies are aggregated into ganglia, some of which are large and more or less 

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

 ner through the peripheral part of the system. Simple visceral reflexes may be mediated by sym- 

 pathetic neurones alone. 



In descriptive anatomy the sympathetic system is regarded as consisting of 

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

 nected by association fibers to form the S3rmpathetic trimk ; (2) central branches 

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

 (Plexus sympathici) with each other and the cerebrospinal nerves; (4) the peripheral 

 ganglia which are interposed in the plexuses (Ganglia plexuum sympathicorum) . 



The S5mipathetic 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 trimk (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 derived 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 derived from the ventral roots of the spinal nerves and terminate in great part 

 about the ceDs of the nearest sympathetic gangUon; others end in more distant or in peripheral 

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

 gangUa, but some are sympathetic fibers which enter the spinal nerve-trunk and terminate about 

 cells of the spinal ganglion. The gray rami consist mainly of non-meduUated fibers derived from 

 the sympathetic gangUa directly or through the 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 nerves. 



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 ganglia, which may be regarded as homologues of 

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



1 The special statements of this description refer to the system of the horse. A few important 

 differential features wiU be mentioned in the account of the nervous system of the other animals. 



