276 



COMPARATIVE ANATOMY. 



definitive urinary bladder and urethra. Indications of the 

 point of exit of the allantois and vitcllo-intestinal duct (umbilical 

 cord) from the body-cavity can be seen in the adult at the navel, 

 or umbilicus, Avhich represents the last point at which the 

 body-walls become united. 



PC(CLf) 



FIG. 220. DIAGRAMMATIC SECTION THROUGH THE HUMAN GUAVID UTERUS. 



U, uterus ; T/>, Tb, Fallopian tubes ; UIT, uterine cavity ; Dv, cleeidua vera, which 

 at Pu passes into the uterine portion of the placenta ; 7V, decidna rellcxa ; Pf, 

 f<etal portion of the placenta (chorion frondosuni, Clif) ; Chi, chorion Iteve ; A, .1, 

 the cavity of the anniion filled with lluid : in the interior of the amnion is seen 

 the embryo suspended by the twisted umbilical cord ; //, heart ; A, ami a ; 

 cs, precaval ; <!, postcaval ; p, portal vein ; At, allantoic (umbilical) artcrio : 

 f, the liver, perforated by the umbilical vein ; D, the remains of the yolk-sac 

 (umbilical vesicle). 



The branchial vessels never become functional as such, in any 

 period of development either in Mammalia or Suuropsida, but those 

 which persist give rise to important vascular trunks of the neck, 

 head (carotids), upper extremity (subclavian), and lungs (pulmonary 

 artery), and also to the roots of the aorta, one or both of which m;iy 

 remain (comp. Fig. 221, A to D). 



