1 8 2 HISTOLOGY 



ganglia. It sends its fibers toward the heart, where they follow the 

 coronary vessels in their ramifications. The cardiac ganglion is asso- 

 ciated with the superficial part of the cardiac plexus, and is under 

 the arch of the aorta. Other small ganglia occur on the posterior wall 

 of the atria, and scattered ganglion cells are found along the atrio-ven- 

 tricular bundle. They have been reported along the nerves elsewhere in 

 the heart. The ganglion cells are probably in connection with efferent 

 fibers from the central nervous system, which include two sorts fibers 

 from the ventral ramus of the accessory nerve, which pass out with the 

 branches of the vagus and inhibit cardiac action; and fibers from the 

 spinal nerves, by way of the inferior cervical ganglion, which accelerate it. 

 Histologically nerve endings have been seen both within and around the 

 capsules of cardiac ganglion cells. It is said that the medullated nerve 

 fibers from the central system end within the capsules; and that non- 

 medullated branches from adjacent sympathetic ganglia end outside of 

 them. Motor endings in contact with cardiac muscle have also been 

 found. Sensory endings have been described both in the epicardium 

 and endocardium. They consist of terminal ramifications forming "end- 

 plates." Some of these fibers presumably connect with sympathetic 

 cells near at hand; others are terminations of afferent medullated fibers 

 which are said to pass to the medulla, along the vagus trunk, as the 

 "depressor nerve." 



LYMPHATIC VESSELS. 



GENERAL FEATURES. The lymphatic vessels are far less conspicuous 

 than the blood vessels, but they are no less important and are widely 

 distributed throughout the body. Those which occur in the mesentery 

 and are filled with a milky fluid after intestinal digestion has been going 

 on, are the most conspicuous. These "arteries containing milk" were 

 observed by Erasistratus, an anatomist of Alexandria who died in 280 

 B. C., but the observation was discredited by Galen. When Aselli in 

 1622 found the white vessels in a living dog which he had opened, and had 

 shown by cutting into them that they were not nerves, it was essentially 

 a new and great discovery. Aselli observed that the vessels were filled 

 only after digestion, at other times being scarcely visible. He traced 

 them to a mass of lymph glands which he mistook for the pancreas, and 

 believed that they passed on into the liver (De lactibus sive lacteis 

 venis, 1627). Years before the physiological observations of Aselli, 

 Eustachius (who died in 1574) had described the main trunk of the 

 lymphatic system in his treatise on the azygos vein (De vena sine 

 pari, Syngramma XIII, Opusc. anat., 1707). He states that from the 

 posterior side of the root of the left jugular vein (Fig. 174) "a certain 



