308 CIRCULATION. 



competent to assist the circulation. 1 The only regular move- 

 ments which occur are seen in the vessels in immediate prox- 

 imity to the right auricle, which are provided with a few 

 fibres similar to those which exist in the walls of the heart. 



Nerves, chiefly from the sympathetic system, have been 

 demonstrated in the walls of the larger veins, but have not 

 been followed out to the smaller ramifications. 



Valves of the Veins. The discovery of the valves of the 

 veins has already been alluded to in connection with the his- 

 tory of the discovery of the circulation. They had undoubt- 

 edly been observed in various parts of the venous system by 

 Cananius, and found very generally distributed throughout 

 this system by Piccolomini, the last named anatomist having 

 published an account of them in 1586 ; but Fabricius, the 

 greatest anatomist of his day, had the good fortune to dem- 

 onstrate them to his illustrious pupil William Harvey, 

 whose immortal discovery indicated their physiological im- 

 portance. Being ignorant of the observations of his prede- 

 cessors on this subject, Fabricius announced himself as their 

 discoverer, and is generally so regarded. In all parts of the 

 venous system, except, in general terms, in the abdominal, 

 thoracic, and cerebral cavities, there exist little membranous 

 semilunar folds, resembling the aortic and pulmonic valves of 

 the heart. "When distended, the convexities of these valves 

 look toward the periphery. In the great majority of instances 

 the valves exist in pairs, but are occasionally found in groups 

 of three. They are formed of the delicate lining membrane 

 of the veins, with the internal or longitudinal layer of the 

 middle coat. Some transverse fibres are found around the 

 base of the valves, and a few muscular fibres have been 



1 This statement applies particularly to the human subject. Schiff has noticed 

 rhythmical contractions of the veins in the ear of a rabbit (LONGET, Traite de 

 Physiologic, Paris, 1861, tome i., p. 876), and Mr. Wharton Jones has observed 

 the same phenomenon in the wing of the bat (TODD and BOWMAN, Physiological 

 Anatomy, Am. ed. 185*7, p. 703, note). There is no evidence that this is general. 

 or that it has any influence in favor of the circulation. 



