From the large superior cervical nerve ganglion the sympathetic trunk extends downward toward the thorax. It is covered deeply with muscles. This portion is known as the cervical sympathetic nerve trunk. A trunk lies on each side of the cervical vertebræ. The large thoracic nerve ganglion, the inferior cervical, is located along this trunk at the entrance of the thorax. From this ganglion there is given off the recurrent cardiacus which supplies the heart. The end branches of the sympathetic nerve trunk blend with the pneumogastric nerve. The inferior nerve ganglion is the ganglion cardiacum. Near this ganglion is found a nerve plexus in which there are imbedded peripherlistic ganglia. This thoracic plexus, accompanying the collica artery, passes to the abdominal region, supplying the intestines and taking part in the formation of the abdominal plexus. The abdominal plexus is located near the anterior portion of the kidneys. Its fibers are directed mainly downward to the visceral organs. The large intestine, the rectum and the copulatory organs receive branches. These latter branches take part in the formation of the pedunda nerve plexus. Some branches of this plexus, follow the branches of the posterior mesenteric artery. The _thoracic trunk_ (Fig. 64, No. 42) of the sympathetic is double. The anterior portion gives off an anterior splanchnic nerve, or plexus (Fig. 64, No. 43) which accompanies the celiac axial artery to the gizzard and liver, communicating with the pneumogastric. The posterior splanchnic nerve is intimately combined with the adrenal body, and the testes, or the ovary (Fig. 64, No. 45). Intestinal branches accompany those of the mesenteric arteries (Fig. 64, No. 46). Other branches supply the kidneys, and communicate with long branches of the spinal nerves destined for the cloaca and adjacent parts, and thus form a plexus similar to that found in mammals. FUNCTIONS OF THE NERVOUS SYSTEM According to function, the nerves composing the trunks are divided into afferent and efferent. The _afferent nerves_ are those that convey the impulses from the periphery of the body to the nerve center, which are located in the brain or in the spinal cord. The impulses conveyed are those of special senses, as sight, hearing, taste, touch, and smell. Impulses producing sensation pleasurable or painful come from the skin, the muscle, or the viscera. The _efferent nerves_ are those which convey impulses from the nerve centers to the periphery. These impulses may be motor as those going to the muscle cells of the skeletal muscles, the viscera, or the blood-vessels. These motor impulses make movements in these organs possible. In the blood-vessel they result in the control of the caliber of the vessel. These impulses may be of an inhibitory character, as in slowing the heart. They may be secretory impulses stimulating the gland to activity or regulating metabolism.