VASCULAR SYSTEM OF FCETUS. 765 



have a similar arrangement; the more superficial and longer turning inwards, 

 and including the deeper and shorter bands. All these fibres ascend and spread 

 out upon the inner surface of the ventricles, forming the walls, the septum, and 

 the musculi papillares, which project from these cavities ; and they are finally 

 inserted into the auriculo-ventricular fibrous rings directly, or, indirectly, 

 through the chordae tendineas. Of these spiral fibres, some enter at the inter- 

 ventricular furrows, and surround either ventricle singly ; others pass across 

 the furrows and embrace both cavities. On tracing those which form the vortex 

 back into the interventricular septum, they are found to be interlaced with 

 similar fibres from the right ventricle, and ascend vertically upon the right side 

 of the septum, as far as its base, in the form of a long and broad band. 



Circular fibres. The circular fibres are situated deeply in the substance of 

 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 fur- 

 row. 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 left or anterior 

 and the right or posterior 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 veure 

 cordis minima? (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 cranial nerves, and partly from the sympathetic. They are freely 

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

 filaments being furnished with small ganglia. 1 



PECULIARITIES IN THE VASCULAR SYSTEM OF THE FCETUS. 



The chief Peculiarities in the Heart of the Foetus are the direct communica- 

 tion between the two auricles through 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 



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 ven- 

 tricles 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 auricu- 

 larurn, forming a communication between the auricles. 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 into the auricle. It is directed upwards on the left 

 side of the opening of this vein, and 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 part of the arch of the aorta, by 

 means of the ductus arteriosus, and the communication between the internal 

 iliac arteries and the placenta, by means of 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. In the early condition, it forms the con- 



1 For full and accurate descriptions of the nerves and ganglia of the heart, the student is 

 referred to Dr. R. Lee's papers on the subject. 



