THORACIC TRUNCUS SYMPATHICUS 407 
ANATOMY 
Truncus sympathicus. In the cat the thoracic portion of the 
sympathetic trunk presents an arrangement of its ganglia and 
branches somewhat different from that found in man. The 
chief differences are in the fusion of the upper thoracic ganglia 
to form the ganglion stellatum and in the mode of origin of the 
splanchnic nerves. The trunk lies along the sides of the bodies 
of the vertebrae ventral to the heads of the ribs, and consists of a 
series of ganglia, for the most part segmentally arranged, bound 
together by a continuous nerve cord. Each spinal nerve is con- 
nected with an adjacent ganglion by a gray ramus. A ganglion 
may send a gray ramus to two or more nerves, in which case it 
represents a combination of two or more segmental ganglia. 
Some compound ganglia are constant in their occurrence, as in 
the case of the stellate and the superior cervical ganglia; others 
may occur occasionally in any part of the trunk due to the fusion 
of two segmental ganglia. Thus the segmental character of the 
truncus is indicated by the gray rami, although in some cases 
adjacent segments may be fused. The white rami are much more 
irregular in their distribution. From all this it will be apparent 
that the best method of designating the ganglia is by giving 
them the number of the spinal nerve to which they are connected 
by their gray ramus. The facts concerning the connections of 
the fibers of the gray and white rami, which will be detailed later 
in this paper, also bear out this conclusion. Langley (’91 a) has 
made use of the same method of designating the ganglia. When 
we speak of the twelfth thoracic ganglion we shall have in mind 
the ganglion whose gray ramus runs to the twelfth thoracic 
nerve, although a glance at figure 1 will show that there are less 
than twelve separate ganglia in the thoracic region, and that this 
particular ganglion usually receives a white ramus from the 
eleventh thoracic nerve. The portion of the continuous nerve 
cord which joins two successive ganglia together we shall speak 
of as an internodal segment and shall number the successive 
segments to correspond to the numbers of the ganglia below which 
they lie. 
