THE SYMPATHETIC NERVE. 799 



In the neck they are situated in front of the transverse processes of the verte- 

 brae ; in the dorsal region, in front of the heads of the ribs ; in the lumbar region, 

 on the sides of the bodies of the vertebrae ; and in the sacral region, in front of the 

 sacrum. As the two cords pass into the pelvis they converge and unite together 

 in a single ganglion (ganglion impar) placed in front of the coccyx. Each 

 ganglion may be regarded as a distinct centre, and, in addition to its branches of 

 distribution, possesses also branches of communication which communicate with 

 other ganglia and with the cerebro-spinal nerves. 



The branches of communication between the ganglia are composed of gray 

 and Avhite nerve-fibres, the latter being continuous with those fibres of the spinal 

 nerves which pass to the ganglia. 



The branches of communication between the ganglia and the cerebro-spinal 

 nerves also consist of white and gray nerve-fibres, which may be contained in 

 separate filaments or united in a single branch ; the former proceeding from the 

 spinal nerve to the ganglion, the latter passing from the ganglion to the spinal 

 nerve, so that a double interchange takes place between the two systems. While 

 gray communicating fibres pass from all the sympathetic ganglia to all the spinal 

 nerves, it would appear that the white communicating fibres from the spinal nerves 

 to the sympathetic only exist in the dorsal and upper lumbar regions. 



The three great gangliated plexuses are situated in front of the spine in the 

 thoracic, abdominal, and pelvic regions, and are named, respectively, the cardiac, 

 the solar or epigastric, and the hypogastric plexus. They consist of collections of 

 nerves and ganglia, the nerves being derived from the gangliated cords and from 

 the cerebro-spinal nerves. They distribute branches to the viscera. 



Smaller ganglia are also found lying amidst the nerves, some of them of 

 microscopic size, in certain viscera as, for instance, in the heart, the stomach, and 

 the uterus. They serve as additional centres for the origin of nerve-fibres. 



The branches of distribution derived from the gangliated cords, from the 

 prevertebral plexuses, and also from the smaller ganglia, are principally destined 

 for the blood-vessels and thoracic and abdominal viscera, supplying the involuntary 

 muscular fibre of the coats of the vessels and the hollow viscera, and the secreting 

 cells, as well as the muscular coats of the vessels in the glandular viscera. 



THE GANGLIATED CORD. 

 Cervical Portion of the Gangliated Cord. 



The cervical portion of the gangliated cord consists of three ganglia on each 

 side, which are distinguished, according to their position, as the superior, middle, 

 arid inferior cervical. 



The Superior Cervical Ganglion, the largest of the three, is placed opposite the 

 second and third cervical vertebrae. It is of a reddish-gray color, and usually 

 fusiform in shape, sometimes broad and flattened, and occasionally constricted at 

 intervals, so as to give rise to the opinion that it consists of the coalescence of 

 several smaller ganglia ; and it is usually believed that it is formed by the coales- 

 cence of the four ganglia corresponding to the four upper cervical nerves. It is 

 in relation, in front, with the sheath of the internal carotid artery and internal 

 jugular vein; behind, it lies on the Rectus capitis anticus major muscle. 



Its branches may be divided into superior, inferior, external, internal, and 

 anterior. 



The superior branch appears to be a direct prolongation of the ganglion. It 

 is soft in texture and of a reddish color. It ascends by the side of the internal 

 carotid artery, and, entering the carotid canal in the temporal bone, divides into two 

 branches, which lie, one on the outer, and the other on the inner, side of that vessel. 



The outer branch, the larger of the two, distributes filaments to the internal 

 carotid artery and forms the carotid plexus. 



The inner branch also distributes filaments to the internal carotid, and, con- 

 tinuing onward, forms the cavernous plexus. 



