AND PREGNANCY. 357 



child has usually its own amnion, whereas there is a 

 common chorion.* 



571. The medium of connection between the mother 

 and child, are the umbilical chord and the placenta into 

 which it is distributed. 



572. The umbilical chord, which appears coeval with 

 the embryo, varies exceedingly in length and thickness, 

 in the place of its insertion into the placenta, in its va- 

 ricose knots, &c. It generally consists of three blood 

 vessels twisted spirally together, viz. a vein running to 

 the liver of the foetus, and two arteries arising from its 

 internal iliacs or hypogastrics. They are separated from 

 each other by cellular septa of various directions, f and 

 are throughout narrowed internally by nodules or the 

 quasi-valves of Hoboken. | 



They are collected into a chord by means of a cel- 

 lular membrane, which is full of a singular very limpid 

 fluid called Whartonian, resembling gelatine in appear- 

 ance, and is surrounded externally by a continuation 

 of the amnion. 



573. At the part of the chord which is united to the 

 foetus, there runs the urachus, which arises from the 

 fundus of the urinary bladder and lies between the two 

 umbilical arteries. In the human subject, it is pervious 



* See Denman, Engravings tending to illustrate generation and parturition. 

 Lond. 1787. fol. tab. ix. 



Twins are very rarely contained in a common amnion. Vide J. de Puyt, 

 Vtrhandel. der Zeeuwsch Genootsch. te Ulissingen. T. ix. p. 423 sq. 



f- W. Noortwyk, Uteri Humani Gravidi Anatome. tab. iii. fig. 5, 6, 7. 



J Hoboken, Anatome secundin. human, repetita. p. 522 sq. fig. 38, 39, 40. 



This structure is further displayed in the arterial branches of the placenta by 

 Aug. Chr. Reuss, Nov. Observ. circa Structur. Vasor. in Placenta Humana. 

 Tubing. 1784. 4to. 



J. Noreen, De Uracho. Getting. 1749. 4to. 



Ph. Ad. Boehmer on the same, at the end of his Anatomt ovi hum, 

 ted dtformis. Hal. 1763. 4to. 



