942 



OF GENERATION EMBRYONIC DEVELOPMENT. 



whose development is required to be in advance of that of the lower, are 

 supplied with blood nearly as pure as that which returns from the placenta; 



whilst the rest of the body receives a 

 mixture of this with what has previous- 

 % O lv circulated through the system ; and 



of this mixture a portion is transmitted 

 to the placenta, to be renovated by 

 coming into relation with the maternal 



FIG. 347. Diagram of the Foetal Circulation. 1. The 

 umbilical cord, consisting of the umbilical vein and 

 two umbilical arteries, proceeding from the placenta 

 (2). 3. The umbilical vein dividing into three branches ; 

 two (4, 4) to be distributed to the liver, and one (5), the 

 ductus venosus, which enters the inferior vena cava(6). 

 7. The portal vein, returning the blood from the intes- 

 tines, and uniting with the right hepatic branch. 8. 

 The right auricle; the course of the blood is denoted 

 by the arrow proceeding from 8 to 9, the left auricle. 

 10. The left ventricle; the blood following the arrow 

 to the arch of the aorta (11), to be distributid through 

 the branches given off by the arch to the head and 

 upper extremities. The arrows 12 and 13 represent the 

 return of the blood from the head and upper extrem- 

 ities through the jugular and subelavian veins, to the 

 superior vena cava (14), to the right auricle (S), and in 

 the course of the arrow through the light ventricle 

 (15), to the pulmonary artery (16). 17. The ductus 

 arteriosus, which appears to be a proper continuation 

 of the pulmonary artery; the offsets at eacli side are 

 the right and left pulmonary arteries cut off. The 

 ductus arteriosus joins the descending aorta (18,18), 

 which divides into the common iliacs, and these into 

 the internal iliacs, which b-.-cunu- the umbilical aiteries 

 (19), and return the blood along the umliili -;il cord to 

 the placenta, and the external iliacs (20), which are 

 continued into the lower extremities. The arrows at 

 the termination of these vessels mark the return of the 

 venous blood by the veins to the inferior cava. 



fluid. At birth the course of the current is entirely changed by the cessa- 

 tion of the circulation through the Placenta, and by the enormous increase 

 in the quantity transmitted to the Lungs, which takes place immediately on 

 the first inspiration: the Ductus Venosus and Ductus Arteriosus soon shrivel 

 into ligaments; the Foramen Ovale becomes closed by its valve; and the 

 circulation which was before carried on upon the plan of that of the higher 

 Reptiles, now becomes that of the complete Bird or Mammal. 1 It is by no 

 means unfrequent, however, for some arrest of development to prevent the 

 completion of these changes; and various malformations, involving an im- 

 perfect discharge of the function, may hence result. From the above descrip- 

 tion it is obvious that the chief propelling power in the circulation of the 

 Foetus is the right heart; the force of the left heart being chiefly spent in 

 propelling a due supply of blood to the head and upper extremities; and an 

 interesting observation of Langer' 2 is in accordance with this, for he has 

 shown that the walls of the right ventricle in the fu-tus are as thick as those 

 of the left, whilst those of the right auricle are even thicker and more mus- 



1 Kur causes of closure of the Ductus Arteriosis, see VValkhoff, llenle and Pfeili'er's 

 Zeitschrift, Bd. xxxvi, p 109. 



/ur Anatomic der Fotalcn Kreislaufor^ane, Zc'its. der Gesell. d. Wicn, xiii, p. 



u o 



