664 THE NERVOUS SYSTEM. 
the spinal nerves. These gray rami are found in connexion with each and all of 
the spinal nerves. Their origin from the gangliated cord is irregular: they may 
come from the ganglia or the commissure; they may divide after their origin, so 
that two spinal nerves are supplied from one ganglion ; or two ganglia may supply 
branches to a single spinal nerve. In relation to the spinal nerve, the gray ramus 
is distributed along the somatic divisions of the nerve, supplying branches to the 
unstriped muscular fibres (vaso-motor, pilo-motor) and glands (secretory). They 
also provide small recurrent branches, ending in the membranes enveloping the 
spinal nerve-roots. Mingled with the non-medullated fibres of the gray rami 
are found a small number of medullated fibres, regarded as medullated sym- 
pathetic fibres, and axons from the dorsal spinal ganglia incorporated with this 
ramus. 
The commissural cords of the sympathetic system are composed of white and 
gray fibres. The white fibres are: (1) Splanchnic efferent fibres, passing to a 
ganglion above or below the point of entrance into the sympathetic system; (2) 
splanchnic afferent fibres, guided along the commissure and over or through the 
gangha. The gray fibres are the axons of sympathetic ganglion cells: (1) true 
commissural fibres passing into connexion with the cells of a neighbouring 
ganglion ; (2) fibres passing along the commissure for a certain distance upwards 
or downwards before entering the splanchnic area as peripheral branches. 
The peripheral (splanchnic) branches from the sympathetic cord consist of— 
(1) white fibres—splanchnie afferent fibres unconnected with cells, and splanchnic 
efferent fibres which, after passing over the gangliated cord, are on their way to 
join peripheral (collateral) or terminal ganglia in relation to the viscera ; and of (2) 
gray fibres, splanchnic efferent branches, the axons of sympathetic ganglion cells 
distributed to the vessels and viscera in the splanchnic area. 
THE CERVICAL PART OF THE SYMPATHETIC CORD. 
The cervical part of the sympathetic cord may be regarded as an upward 
prolongation of the primitive sympathetic system along the great vessels of the 
neck. It is characterised by the absence of white rami communicantes connecting 
it with the cervical spinal nerves. Its spinal fibres ascend from the upper 
thoracic nerves in the commissural cord, and are connected with the cells of the 
cervical ganglia. The branches from the ganglia in the neck are distributed to 
structures in the head, neck, and thorax: (1) motor fibres to involuntary muscles 
(e.g. dilator of the pupil); (2) vaso-motor fibres along the arteries of the head and 
neck and upper limbs; (3) pilo-motor fibres along the cervical spinal nerves to the 
skin of the head and neck; (4) cardio-motor fibres; (5) and secretory fibres (for 
the submaxillary gland). 
The ganghated cord in the neck is placed upon the prevertebral muscles 
behind the carotid arteries. It extends from the root of the neck, where it is con- 
tinuous behind the subclavian artery with the thoracic portion of the cord, to the 
base of the skull, where it ends in the formation of plexiform branches upon the 
internal carotid artery. It consists of a narrow commissural cord composed of 
medullated and non-medullated fibres, on which are two or three ganglia—a 
superior ganglion at the upper end, an inferior ganglion at the point of junction 
with the thoracic portion of the cord, and an intermediate middle ganglion varying 
in position and not always present. 
The superior cervical ganglion (g. cervicale superius) is placed near the base of the 
skull, between the internal jugular vein and the internal carotid artery. Irregular 
in shape, it is the largest of the sympathetic ganglia, measuring three-quarters 
of an inch or more in length. The commissural cord connects it with the middle 
ganglion (g. cervicale medium), which is of small size, is frequently absent, and may 
be divided into two parts. It is usually placed over the inferior thyroid artery as 
it crosses behind the carotid sheath. 
The inferior ganglion (g. cervicale inferius) is joined by the commissural cord to 
the middle (or superior) ganglion above, and is imperfectly constricted off from the 
first thoracic ganglion below. It is of considerable size, irregular in shape, and is 
ail 
