106 FCETAL CIRCULATION. 



blood to the placenta. These in the adult are closed and 

 become the superior ligaments of the bladder. 



3d. The umbilical vein, which carries the blood from the 

 placenta to the foetus, is in the adult obliterated; that por- 

 tion between the umbilicus and the liver, becoming the 

 round ligament of the liver ; while the remaining portion 

 connecting with the hepatic vein, and thence with the vena 

 cava inferior, is the closed cord of the ductus venosus. 



4th. The placenta, which, after birth, is detached from 

 the umbilical cord. 



The human placenta is described as consisting of two 

 portions, the one belonging to the foetus, the other to the 

 uterus of the mother; dense tufts of vascular villi compose 

 the foetal portion, while the maternal portion is formed of 

 the decidua of the uterus, which receives the foetal villi 

 thus formed, it is the medium of nourishment to the foetus 

 during the period of utero-gestation. 



CHAPTER IV. 



THE NERVOUS TISSUE. 



ANALYSIS. 



IMPORTANCE, DIVISIONS ACCORDING TO BICHAT, SITUATION, EXTENT, SYM- 

 METRY, DIVISIONS ACCORDING TO DEVELOPMENT, COMPOSITION, 

 FUNCTIONS, RELATIONS. 



THE nervous system, says M. Cuvier, constitutes the ani- 

 mal, and the other systems are provided in order to serve 

 and maintain it. It is regarded as presiding over all the 

 functions of the body, as being the source of all sensation 

 and motion, as regulating the temperature and controlling 

 the different secretions. The importance of this tissue 

 then, cannot be too highly estimated as forming one of the 

 fundamental elements entering into the constitution of the 

 several organs. According to Bichat, it is divided, 



1. Into the nervous system of animal life. 



2. The nervous system of organic life. 



