254 OUTLINES OP EQUINE ANxiTOMY. 



between two of tlie divisions of lobulus scissatus, where it 

 breaks np, and its blood, after ramifying througli the liver 

 (which is very large in the foetus), as in the adult, gains 

 the posterior vena cava through the hepatic veins. It 

 thus passes to the heart, and the major portion of it 

 through the foramen ovale in the septum auricularum 

 into the left auricle, where it meets with blood from the 

 lungs, and with it through the left ventricle passes into the 

 aorta, and from that into the anterior aorta, for the pos- 

 terior aorta is mainly occupied by another current. The 

 blood which gained the right auricle from the anterior vena 

 cava, though a small amount of it passes through foramen 

 ovale, for the most part having traversed the right ven- 

 tricle, gains the pulmonary artery, from which some passes 

 to the lungs, but a considerable portion through the ductus 

 arteriosus, a vessel connecting the pulmonary artery to the 

 posterior aorta. Through the posterior aorta some passes 

 to the body of the foetus and some through the uterine 

 arteries to be reoxygenated in the chorion. Foramen ovale 

 is an opening through septum auricularum just in front of 

 the termination of the posterior vena cava ; it is guarded 

 by a valve formed of a double fold of endocardium. After 

 birth it becomes obliterated on the left side, traces of it 

 remaining on the right side, forming the fossa ovalis sur- 

 rounded by a prominent yellow ring, annulus ovalis. 



Immediately, but loosely, surrounding the foetus in utero 

 is the amnion. This is a thin membrane which presents 

 some extremely convoluted vessels, ramifying over its 

 surface, and serves to secrete a fluid in which the foetus 

 floats (liq[UOr aninii) . It is contmuous with the skin of 

 the foetus at the umbilicus, becoming reflected over that 

 portion of the umbilical cord nearest to this opening, and 

 which is therefore termed the amniotic portion. Floating 

 about in the liquor amnii generally are one or more 

 brownish masses of soft substance. These are the hippo - 

 manes, and are supposed to be composed of nutritious 

 matter. Sometimes they are attached to the inner sur- 

 face of the amnion. In this country they are generally 

 termed ''false tongues,'' from their peculiar shape. 



Investing the amnion, and lining the chorion, is a serous 

 membrane, the allantois. Its parietal or cJiorial fortiori is 

 continuous with its visceral or amniotic portion by a portion 

 reflected over that part of the umbilical cord which ex- 



