MODE OF CONNECTING THE MATEENAL WITH THE FCETAL CIRCULATION. 



The circulation of maternal blood in the uterine and placental sinuses is the 

 same in principle as that for circulating air in the lungs, namely, by rhyth- 

 mical changes in pressure in the sinuses, which is produced by the action taking 

 place in the womb itself ; taking the placental sinuses to represent the alveoli, 

 and the uterine the tracheal system, the blood flowing in and out of this system 

 of canals by^reflux action for renewal, just as the pulinonic air flows in and out 

 of the tracheal system for renewal, only that in the former the fluid passes into 

 the venous system of the mother and is returned by the arterial, both terminat- 

 ing by capillary openings in the canals, while the placental souffle answers to 

 the respiratory murmur. 



We have already spoken of the role which the placenta plays in this respect, 

 and it now remains to take up the very important one which the uterus itself 



FIG. 3. LONGITUDINAL SECTION OF A LATELY GRAVID WOMB, showing the canal system. 

 Taken from a case of post partem bffimorihage (partly diagrammatic). 1, peritonieum ; 2, 

 uterine canals (sinuses); 3, openings to canals on the mucous surface corresponding with 

 openings to placental sinuses; g, Fallopian tube; /, ligament toTtrtCTyr-r, round ligament. 



(fir-tv^^l 



performs for completing this deeply-interesting mechanics, which it would be 

 difficult to overestimate, underlying, as it does, embryonic life. 

 First, with regard to the uterine sinuses, we may mention that this canal 



