VASCULAR SYSTEM OF THE FOETUS. 699 



the heart ; towards the base they enter the anterior and posterior longitudinal 

 furrows, so as to include each cavity singly, or, passing across them, surround 

 both ventricles, more fibres passing across the posterior than the anterior furrow. 

 They finally ascend in the substance of the ventricle, to be inserted into the fibrous 

 rings at its base. 



Vessels and Nerves. The arteries supplying the heart are the anterior and pos- 

 terior coronary. 



The veins accompany the arteries, and terminate in the right auricle. They are 

 the great cardiac vein, the small or anterior cardiac veins, and the vena3 cordis 

 minimae (vense Thebesii). 



The lymphatics terminate in the thoracic and right lymphatic ducts. 



The nerves are derived from the cardiac plexuses, which are formed partly from 

 the spinal, and partly from the sympathetic system. They are freely distributed 

 both on the surface, and in the substance of the heart ; the separate filaments being 

 furnished with small ganglia. These have been figured by Kemak, but the more 

 extended investigations of Dr. Eobert Lee have shown them \p exist in great 

 abundance, both in the nerves distributed to the surface, and in those in the 

 interior of the organ. 



PECULIARITIES IN THE YASCULAR SYSTEM OF THE FOETUS. 



The chief peculiarities in the heart of the foetus are the direct communication 

 between the two auricles by the foramen ovale, and the large size of the 

 Eustachian valve. There are also several minor peculiarities. Thus, the position 

 of the heart is vertical until the fourth month, when it commences to assume an 

 oblique direction. Its size is also very considerable, as compared with the body, 

 the proportion at the second month being as 1 to 50 : at birth, it is as 1 to 120 : 

 whilst, in the adult, the average is about 1 to 160. At an early period of foetal 

 life, the auricular portion 'of the heart is larger than the ventricular, the right 

 auricle being more capacious than the left ; but, towards birth, the ventricular 

 portion becomes the larger. The thickness of both ventricles is, at first, about 

 equal ; but, towards birth, the left becomes much the thicker of the two. 



The foramen ovale is situated at the lower and back part of the septum 

 auricularum. Through it the auricles communicate with each other. It attains 

 its greatest size at the sixth month. 



The Eustachian valve is developed from the anterior border of the inferior vena 

 cava, at its entrance in the auricle, and, rising up on the left side of the opening 

 of this vein, serves to direct the blood from the inferior vena cava through the 

 foramen ovale into the left auricle. 



The peculiarities in the arterial system of the foetus are the communication 

 between the pulmonary artery and descending aorta, by means of the duct us 

 arteriosus, and the communication between the internal iliac arteries and the 

 placenta, by the umbilical arteries. 



The ductus arteriosus is a short tube, about half an inch in length at birth, and 

 of the diameter of a goose-quill. It connects the left branch of the pulmonary 

 artery with the termination of the arch of the aorta, just beyond the origin of the 

 left subclavian artery. It conducts the chief part of the blood of the right ventri- 

 cle into the descending aorta. 



The umbilical or hypogastric arteries arise from the internal iliacs, in addition 

 to the usual branches given off from these vessels in the adult. Ascending along 

 the sides of the bladder to its fundus, they pass out of the abdomen at the 

 umbilicus, and are continued along the umbilical cord to the placenta, coiling 

 round the umbilical vein. They return the blood to the placenta which has been 

 circulated in the system of the foetus. 



The peculiarity in the venous system of the foetus is the communication 

 established between the placenta and the liver and portal vein, through the 

 umbilical vein, and with the inferior vena cava by the ductus venosus. 



