680. ' PHILOSOPHICAL TRANSACTIONS. [aNNOIJOI. 



- one towards the other did not mix, but remained distinct. This observation 

 fully satisfied that great anatomist, as to the existence of an allaiitois ; and its 

 figure, texture, site, &c. might also have been discovered by him, had not 

 the less curious spectators been impatient to pass on to other parts of the 

 dissection. 



Some deny a urinary membrane to a human foetus, because tliey suppose the 

 urachus to be impervious, and that therefore there would be no passage for the 

 urine, consequently no need of an allantois. Needham indeed says that he 

 could never find any sign of a cavity in the urachus; yet is of opinion, tliat by 

 blowing from the bladder, the air might be forced through a human urachus, 

 as easily as he has often done through that of a whelp. I do not understand 

 why Dr. Needham and others should insist so much upon an apparent cavity in 

 the urachus, or expect that air should necessarily pass through it on blowing, or 

 think that otherwise it cannot be fit for the assigned office : since many bodies, 

 as membranes, &c. will not admit air, &c. yet let water pass freely through them. 

 It will not seem strange that water should pass througli the substance of the 

 urachus, if we consider that the cavity of the urachus to the navel is open, as 

 appears by inflation or injections, (to say nothing of those who are mentioned 

 to have made water by the navel,) and that the rest of the urachus is pervious, 

 though not plainly hollow, (the urine rather soaking gently than running 

 through its more straight tubes,) may be gathered from hence : 1st, That the 

 substance of the urachus, as well as the cavity of the allantois, is always found 

 turgid with a liquor, that in colour, taste, and smell, seems to be urinous. 

 2dly, That since the mucous coat of the intestines is demonstrated to be vascular 

 by Mr. Leuwenhoeck, therefore the mucous substance of the urachus may also 

 be vascular. 3dly, That urine may as easily ouse through these mucous vessels, 

 as other fluids run through vascular cartilages, and bones, &c. or the chyle into 

 lacteals, whose orifices as Leuwenhoeck observes, will scarcely admit of parti- 

 cles so large as the 1000000000 part of a grain of sand, the great cavity of the 

 intestines being open at the same time ; or as easily as grosser parts of the semen 

 pass the tubes of the testicles, whose cavities are not more perceptible. I am 

 sure the urine is more assisted in its motion by the detrusor urintB, &c. than any 

 of these fluids can be by the heart or other muscles. 



Others will not admit of a uriuar\' membrane, imagining it would be useless, 

 because they think, that when the bladder is full, the urine must be discharged 

 at its cervix, and not at its fundus, by the urachus. But in answer to this, the 

 urine can never pass through the cervix and urethra, unless the abdonunal 

 muscles contract, because we never void urine naturally but by tiic help o( these 

 muscles, nothing less being able to force open the sphincter vesicae. Now it 



