VOL. XXII.] PHILOSOPHICAL TKANSACTIONS. 581 



being more than probable that tliese muscles never act before respiration, no 

 urine can pass through the sphincter before the child breathes. No reason can 

 be given why the abdominal muscles of a foetus should voluntarily contract, 

 since neither the quantity nor quality of the urine can excite to such an action. 

 For when the bladder is too full of urine it will ouse through the lax spongy 

 substance of the urachus, being gently pressed by the detrusor alone. There 

 would arise many inconveniencies from the voluntary contraction of the abdo- 

 minal muscles of a foetus, as voiding faeces as well as urine into the amnios, 

 which would be more prejudicial than sweat, &c. Yet if we should suppose the 

 abdominal muscles of a foetus to act, the urine will however pass where it can 

 most easily, i. e. through the urachus, which is partly open, and altogether of 

 such a texture as is nowise to hinder the passing of the urine, much less to be 

 able to resist a considerable force, as the sphincter vesicae can. Besides, the 

 urachus is not only thus qualified for the admission of urine, but when the 

 mother lies down, it is almost on a level with the urethra, and what has once 

 passed the urachus cannot return, by reason of the length, situation, and pecu- 

 liar structure of it. Lastly, the pudendi clausura sometimes happening in both 

 sexes, demonstrates, that then at least the urine cannot pass through the 

 urethra. 



Dionis not finding any allantois, nor an urachus plainly pervious, thinks 

 there is no need of either, on another account. For he supposes that the blood 

 which serves for the nutrition of the foetus, is depurated from all excrement. 

 But I cannot apprehend what should make this portion of the blood and chyle 

 freer from excrement than the rest of the mass of blood. There is indeed no 

 portion of it which does not contain parts unfit for assimilation and nutrition. 

 Dionis would have been convinced of this error had he ever opened abortions of 

 five months old, or upwards, their bladders being always full of urine, and some 

 faeces constantly in the intestines. It is difficult to determine when this separa- 

 tion of urine first begins ; but I am apt to think it much sooner th;m is gene- 

 rally supposed. Fig. 1, pi. 15, is the allantois of a very small abortion, wiiich 

 I have still by me. Since all the parts are perfectly formed before impregnation, 

 not very long after it ^fiey may begin to perform their offices. No doubt they 

 begin as soon as there is occasion for any separation, and a separation of urine 

 is necessary when the foetus is first nourished by the umbilical arteries. 



The existence of an allantois is denied by some who grant a urachus, but will 

 have it convey the urine between the amnios and chorion. Diemerbroeck's 

 opinion is somewhat like this, only he would have the urine lodged between the 

 urinary membrane and the chorion. These men do not consider that the urine 

 in this case would get into the amnios as well as the succus nutritius of the 



