78 OBSTETRICAL PHYSIOLOGY. 



vascular ramifications, and render the membrane still more apparent, but 

 not at the points where the vessels have almost become capillaries. If, 

 instead of forcing the air towards the ramifications, it is sent in the 

 contrary direction, it will be seen to pass to that portion of the membrane 

 covering the umbilical cord, and insinuate itself between the amnion and 

 the layer of allantois covering it, thus proving the continuity of the 

 membrane. 



As has been stated, the cavity of this sac is in communication with 

 the interior of the bladder by means of the urachus : a narrow canal in 

 the amniotic portion of the umbilical cord, and which widens at the origin 

 of the allantoidean portion, where its walls are continuous with the 

 amniotic layer of the membrane, as well as the chorial layer^ after being 

 prolonged as a sheath around the cord. These arrangements show the 

 allantoid cavity to be a kind of urinary reservoir or dependency of the 

 bladder, the fundus of which is prolonged in an infundibular manner as 

 far as the umbilicus, to constitute the urachus, which follows the umbili- 

 cal vessels in the amniotic portion of the cord, and ends by forming the 

 allantoid cavity. 



The structure of this membrane is slightly fibrous, with a layer of 

 epithelium ; it is thin and pellucid, and appears to be destitute of vessels 

 at a late period of foetal life. It bears on its surface the umbilical 

 vessels, from the umbilicus to the chorion. 



The allantois contains a fluid — the allantoic liquid — the quantity of 

 which, like that of the amnion, is greatest at an early period. It is then 

 colorless or slightly turbid ; but with the growth of the foetus it gradually 

 assumes a yellowish Jiue, until near parturition, when it is brown. It 

 presents somewhat the same physical properties as the liquor amnii, and 

 contains albumen, osmazone, a nitrogenous mucilaginous matter insoluble 

 in alcohol, a particular principle named allantome, which appears to be 

 the urate of urea, with lactic acid, lactate of soda, and phosphates of 

 soda, lime, and magnesia. Allantoic acid is not found in this fluid in 

 solipeds. In addition to the large percentage of water, there is a notable 

 proportion of sugar at an early epoch of foetal life ; this, however, 

 gradually and finally disappears towards the termination of gestation. 



It is probable that before the foetal circulation is fully established, the 

 allantoid fluid serves to nourish the young creature, but that towards the 

 end of gestation it is a product of the urinary secretion of the foetus. It 

 is certain that as gestation approaches its termination, the renal excretion 

 of the young animal passes from the bladder along the urachus, and 

 deposits near the allantoic orifice of that tube a thick fluid of reddish 

 color, and possessing an urinous odor ; it contains uroerithrrin and hip- 

 puric acid. 



The fluid contains, besides, whitish filaments, and small oval or discoid 

 masses of a brownish color from the size a pea to that of a hen's Qgg, 

 either floating about in the cavity or attached to the allantois by a narrow 

 pedicle. Sometimes they are very numerous, and at other times there is 

 only one. From the fanciful notions attached to them in ancient times, 

 they were named the '''' hippomanesy Usually they have the consistency 

 and elasticity of gluten, are flattened, and are thinner at the border than 

 the centre. Those attached to the allantois are generally pyriform, and 

 their pedicle is narrower as they are more developed : proving that the 

 loose bodies in the fluid were originally appendages of the allantois. It 

 is not improbable that they are inspissated parts of the allantoic fluid 



