BEFORE ANJ) AFTER BIRTH. 399 



after birth, this duct becomes obstructed and converted 

 into a kind of dense ligament. 



630. The blood of the aorta, being destined to return, 

 in a great measure, to the mother, enters the umbilical 

 arteries (572), Avhich pass out on each side of the ura- 

 chus at the umbilical opening, and, after birth, likewise 

 become imperforate chords.* 



631. As the function of the lungs scarcely exists in 

 the foetus, their appearance is extremely different from 

 what it is after the commencement of respiration. They 

 are proportionally much smaller, their colour is darker, 

 their substance denser, consequently their specific gra- 

 vity is greater, so that while recent and sound they 

 sink in water, whereas, after birth, they, cseteris pari- 

 bus, swim upon its surface. f The right lung has the 

 peculiarity of dilating during the first inspiration rather 

 sooner than the left.J The other circumstances attend- 

 ing the commencement of respiration were described in 

 the section upon that function. 



632. From our remarks upon the nutrition of the 

 fretus, it is clear that its alimentary tube and chylo- 

 poietic system must be very peculiar. Thus, v. c. in 

 an embryo a few months old, the large intestines very 



* Haller, Icones niitit. fasc. iv. tab. iii. vi. 



t Here is not the proper place for explaining the conditions under which this 

 occurs, and the cautions therefore requisite in giving an opinion, in a court of 

 justice, founded ou the examination of the lungs. 



Among many other writings, the very important posthumous paper of 

 Wm. Hunter may be consulted in the Medical Observ. and Enquiries. Vol. vi. 

 p. 284 sq. 



t Portal, Mem. de VAcud. iks sc, dc Paris. 176D. p. 555 sq. 



Met/.ger, Dr pultnont dc.rtr "ntt i>i/tiftnun rcspirantc. Regiom. 1783. 4to. 



