THE SYMPATHETIC SYSTEM. 583 



cation from the cerebro-spinal nerves, which, there is every reason to 

 believe, consist of fibres coming from the brain or spinal cord, and pass- 

 ing through the ganglion to form part of the peripheral branches of the 

 sympathetic system. This conclusion is drawn not only from the fact 

 that many of these fibres cannot be shown by microscopic examination 

 either to originate or terminate in the substance of the ganglion, but 

 also from the paralyzing effect produced upon muscular organs supplied 

 with sympathetic fibres, by division of the cerebro-spinal nerve which 

 communicates with its ganglion. This is more particularly shown by 

 the paralysis of the iris following division of the oculomotorius nerve, 

 which gives a motor branch to the ophthalmic ganglion. The numerous 

 branches of communication supplied by the pneumogastric nerve to the 

 cardiac branches of the sympathetic, and to the cardiac plexus itself, 

 afford an equally striking instance of the same kind. 



The ganglia seated upon the spinal and cranial nerve roots are there- 

 fore undoubtedly analogous, in their anatomical relations, with the 

 detached ganglia of the sympathetic system proper ; and the whole of 

 this system may be considered as made up of a set of nervous centres 

 disseminated throughout the great cavities of the body, and of nervous 

 filaments which both receive fibres from the cerebro-spinal centres, and 

 communicate by some of their own with the cerebro-spinal nerves. All 

 the organs in the body, accordingly, are supplied with fibres from both 

 sources ; the difference consisting in the proportions in which one kind 

 or the other are present in particular parts. The cerebro-spinal nerves 

 are supplied in the greatest abundance, and manifest their most striking 

 properties, in the organs and functions of animal life ; those of the sym- 

 pathetic system preponderate in the organs of vegetative life, and in 

 their influence upon the functions of nutrition, secretion, and growth. 



Anatomical Arrangement of the Sympathetic System. The sympa- 

 thetic system consists of a double chain of nervous ganglia, running 

 from above downward along the front and sides of the spinal column, 

 and connected with each other by longitudinal filaments. Each gan- 

 glion is reenforced by motor and sensitive fibres from the cerebro-spinal 

 system, and thus the organs under its influence are brought indirectly 

 into communication with external objects and phenomena. Its nerves 

 are distributed to glands and mucous membranes, many of which are 

 destitute of general sensibility, and to muscular parts which are re- 

 moved from the control of the will. The sympathetic ganglia are 

 situated successively in the head, neck, chest, and abdomen; and in 

 each of these regions are connected with special organs by their fibres 

 of distribution. 



The first sympathetic ganglion in the head is the ophthalmic gan- 

 glion, situated within the orbit of the eye, on the outer aspect of the 

 optic nerve. It communicates by slender filaments with the carotid 

 plexus, and receives a motor root from the oculomotorius nerve, and a 

 sensitive root from the ophthalmic branch of the fifth pair. Its fila- 

 ments of distribution, known as the " ciliary nerves," pass forward upon 



