THE SYMPATHETIC TRUNK 1037 



the sympathetic trunk, and by filaments passing to the ansa subclavia ( Vieussenii) , 

 and it is either blended directly with the first thoracic ganglion or connected with 

 it by a short stout portion of the trunk. It gives rami to the last two cervical 

 nerves and peripheral branches to the vertebral and internal mammary arteries, 

 to the heart, and to the inferior thyreoid plexus. 



Connections. — (1) The rami to the seventh and eighth cervical nerves are grey rami 

 communicantes. 



(2) The branches to the vertebral artery are large and they unite with similar branches 

 from the first thoracic ganghon to form a plexus, the vertebral plexus (fig. 787), which accom- 

 panies the artery into the posterior fossa of the cranium, where it is continued on the basilar 

 artery. The plexus communicates in the neck by delicate threads with the cervical spinal 

 nerves. These are probably meningeal rami. 



(3) The branches to the internal mammary artery form the internal mammary plexus. 



(4) The inferior cardiac nerve may arise from the inferior cervical ganghon, from the first 

 thoracic ganglion, or by filaments from both these ganglia (figs. 787 and 789). It communicates 

 with the recurrent larjiigeal nerve and with the middle cardiac nerve, and passes to the deep 

 part of the cardiac plexus. On the left side it frequently joins the middle cardiac nerve to 

 form a common trunk. 



Construction of the cervical portion of the sympathetic trunk. — This portion of the trunk 

 contains both meduUated and non-meduUated fibres, and a large part of the former are of 

 cranio-spinal origin. In the absence of white rami communicantes to this portion of the sym- 

 pathetic trunk, it is evident that few if any of the cranio-spinal or efferent visceral fibres are 

 contributed to it below the superior ganglion by the cervical region of the spinal cord. Instead, 

 such fibres are known to enter by way of the white rami from the upper thoracic nerves, and 

 to ascend to this portion of the sympathetic trunk. Most of these fibres terminate about the 

 cells of the superior, middle, and inferior cervical ganglia, and these cells in their turn give off 

 sympathetic fibres which pass by way of the branches mentioned above for the cephalic and 

 cervical portions, to their distribution in the structures of the head, neck, and thorax. The 

 efferent visceral fibres which terminate in the superior ganghon especially are among those 

 which mediate — (1) vaso-motor impulses for the head; (2) secretory impulses for the submaxil- 

 lary gland; (3) pilo-motor impulses for the hairs of the face and neck; (4) motor impulses for the 

 smooth muscle of the eyelids and orbit, and (o) dilator impulses for the pupil. The sympathetic 

 or grey fibres in the cervical portion of the sympathetic trunk arise from the cells of the upper 

 thoracic and the cervical ganglia, and are passing either to connect the ganglia with each other 

 or to enter the peripheral branches and proceed to their terminal distribution. 



THE THORACIC PORTION OF THE SYMPATHETIC TRUNK 



The thoracic part of the gangliated trunk runs downward on the heads of the 

 ribs from the first to the tenth, and then passes a little ventralward on the sides 

 of the bodies of the lower two thoracic vertebrse. Above it is continuous with the 

 cervical portion at the root of the neck, dorsal to the vertebral artery. Below it 

 leaves the thorax dorsal to the medial lumbo-costal arch (arcuate ligament), or 

 sometimes dorsal to the lateral lumbo-costal arch, and continues into the lumbar 

 portion of the trunk. It lies behind the costal pleura and crosses over the aortic 

 intercostal arteries. 



The number of ganglia in this part of the trunk is variable. There are 

 usualty ten or eleven, but the first is sometimes fused with the inferior cervical 

 ganglion and occasionally other ganglia fuse. The ganglia are irregularly 

 angular or fusiform in shape, and lie on the head of the ribs, on the costo-vertebral 

 articulations, or on the bodies of the vertebrae. The portions of the trunk 

 connecting the ganglia usually are single, but sometimes they are composed of 

 two or three small cords in juxtaposition. Each ganglion, with the possible 

 exception of the first, receives a white ramus communicans from a thoracic nerve 

 and all give oft" grey rayni communicayiies to these nerves. 



The white rami communicantes, as they approach the sympathetic trunk, 

 quite often appear double, due to the separation of a large portion of their fibres 

 into two main streams, one passing upward in the sympathetic trunk, and one 

 passing downward. Of the white rami from the upper five thoracic nerves, the 

 upward stream of fibres is much larger than the downward, due to the fact that a 

 greater part of the efferent visceral fibers from these nerves are distributed through 

 the cervical portion of the sympathetic trunk, as noted above in the construction 

 of that portion. Usually the white rami from the spinal nerves pass directly to 

 the corresponding ganglia of the trunk, and thus lie in company with the corre- 

 sponding grey rami. Sometimes, however, they may join the intermediate por- 

 tions of the trunk, and in the lower thoracic region especially, a ramus may pass 

 from a nerve to the ganglion corresponding to the nerve above or below. The 



