THE F(KTAL JIEAUr 93*J 



the auricle; and lies in the auriculo-ventricular groove on the posterior surfaee of 

 the heart. Its cardiac orifice with the coronary (Thebesian) valve has already l)een 

 described. Besides tlie tributary veins already named, a small oblique vein of 

 Marshall may sometimes l)e traced from the vestifrialfold to the sinus. This little 

 vein, wliicli is not always pervious or easy of demonstration, never i)ossesses a valve 

 at its orifice, anil like the coronary sinus formed a part of the left su]K'rior vena 

 cava of early f(otal life. The sinus also receives the jiosterior interventricular vein, 

 one or more rigbt auricular branches, and several post-ventricular veins from tlie 

 back of the left ventricle. 



The cardiac nerves descend into the su})erior mediastinum, passing in front of 

 and behind the arch of tlie aorta, to unite in the formation of the superficial and 

 deep cardiac plexuses. 



The deep cardiac plexus, the larger and more important, is placed immecliately 

 above the ])ulmonarv artery at its jioint of division, lying between the trachea and 

 arch of tlu^ aorta. It is usually tormed by the interlacement of all the cardiac 

 branches, with the excei)tion of the left sui)erior cardiac branch from the sym- 

 pathetic and the left inferior cardiac from the pneumogastric. 



A mesh work of branches descends from the plexus, some passing to the riglit 

 and some to the left. The greater number of the right l>ranches follow the course 

 of the right coronary artery to form the right coronar}' plexus; some, however, 

 pass forwards to enter the superficial cardiac plexus. 



The left branches, which are both larger and more numerous, descend beneath 

 tlie corresponding pulmonary artery to join the left coronary plexus; some of these 

 pass right and left to join thf anterior pulmonary plexuses at the roots of the lungs. 



The superficial cardiac plexus, which lies in front of the right pulmonary 

 artery as it passes beneath the arch of the aorta, is formed Ijy the interlacement of 

 the left superficial cardiac l>ranch from the sympathetic, the inferior cardiac from 

 the pneumogastric, togctlicr with branches derived from the deep plexus. A small 

 ganglion, the cardiac ganglion of Wrisberg, is sometimes found close to the right 

 side of the ductus arteriosus. The greater numl)er of the filaments from this plexus 

 go to the right coronary jjIcxus. Some, however, reach the left anterior pulmonary 

 plexus. 



The coronary plexuses follow the course of the vessels, and their filaments 

 enter the muscular walls of tlie lieart. Minute ganglia are connected with these 

 filaments, and are especially abundant near the auriculo-ventricular groove. 



Peculiakitiks of the F<etal Heai!T 



The foetal heart is at first almost vertical in position, but during the latter half 



of intra-uterine life it gradually assumes the ol)li(jue i)osition it retains in the adult. 



Its weight in relation to the body varies consi<lerab]y. Thus at the second 



The black connecting arrows indicuto the course of the circulation through the head and 

 neck, the upper extremities, the lungs, the liver, ami the lower extremities. 



The red arrows ^linw tlie ilircctinu nf the ciUTeiit from the placenta, tlir(iai:li tlir umbilical 

 vein, ductus venosus (D. V.) ami liver, to the uplter portion of the inferior vena cava. 



The red arrows with the blue tails and the dotted line show the (•(lursf of the impure 

 blood, as it cntfis the right auricle through tlie inferior vena cava, and traverses the foramen 

 ovale, iruided by the Eustachian valve, to gain the left auricle, left ventricle, ;nid aorta, to lie 

 (Hstributed by its eluef branches to the head and neck and upper extremities. 



T'.ie blue arrows are placed on the superior and inferior venae cavae. and .<ome oi' their main 

 tributary trunks. 



The stream derived from the superior cava passes through the right auricle — in front of that 

 already described — to reach tlu' right ventricle ; thence it passes into tiie pulmonary artery (a 

 small portion oidy reaching the lungs through tlie right and left pulmonary luanclio). ductus 

 arteriosus, and descending aorta. 



The stn-am derivcil from tlie inferior cava mixes witli the blood of tlie umbilical vein, and 

 that which lias passed through the liver, beyond the junction of the ihictus venosus and hei»atic 

 veins. 



The blue arrows with the red heads show tlie coui"se of the blood throui:li the descending 

 aorta to the lower extremities, and tlirouLdi tiie umbilical arteries to the i>laci;nta. 



The colours of the arrows roughly indicate the proportion of pure and impure blood to the 

 different parts of the circulation. 



