604 OF REPRODUCTION. 



and held in their places, by the same reflected membrane. The blood is con- 

 veyed into the Placental cavity by the " curling arteries" of the Uterus ; and 

 is returned from it by the large veins, that are commonly designated as 

 sinuses.* The foetal vessels, being bathed in this blood, as the branchiae of 

 aquatic animals are in the water that surrounds them, not only enable the 

 festal blood to exchange its venous character for the arterial, by parting with 

 its carbonic acid to the Maternal blood, and receiving oxygen from it ; but 

 they also serve as rootlets, by which certain nutritious elements of the Ma- 

 ternal blood (probably those composing the liquor sanguinis) are taken into 

 the system of the Foetus. There is no more direct communication between 

 the Mother and Foetus than this ; all the observations which have been sup- 

 posed to prove the existence of real vascular continuity, having been falsified 

 by the extravasation of fluid, consequent upon the force used in injecting the 

 vessels. Moreover, the different size of the blood-corpuscles in the Foetus 

 and in the Parent ( 575) shows the non-existence of any such communication .t 

 750. The formation of the Placenta, in the manner just described, com- 

 mences in the latter part of the second month ; during the third, it acquires 

 its proper character ; and it subsequently goes on increasing, in accordance 

 with the growth of the ovum. Towards the end of the term of gestation, 

 however, it becomes more dense and less vascular ; owing, it would seem, to 

 the obliteration of several of the minuter vessels, which are converted into 

 hard fibrous filaments. The vessels of the Uterus undergo great enlargement 

 throughout, but especially at the part to which the Placenta is attached ; and 

 the blood in moving through them produces a peculiar murmur, which is 

 usually distinctly audible at an early period of Pregnancy, and may be re- 

 garded (when due care is taken to avoid sources of fallacy) as one of its most 

 unequivocal positive signs. The Placental bruit is thus described by Dr. 

 Montgomery.;}: " The characters of this phenomenon are, a low murmuring 

 or somewhat cooing sound, resembling that made by blowing gently over the 

 lip of a wide-mouthed phial, and accompanied by a slight rushing noise, but 

 without any sensation of impulse. The sound is, in its return, exactly 

 synchronous with the pulse of the mother at the time of examination; and 

 varies in the frequency of its repetitions, with any accidental variation which 

 may occur in the maternal circulation. Its situation does not vary during the 

 course of the same pregnancy ; but in whatever region of the uterus it is first 

 heard, it will in future be found, if recognized at all, for it is liable to inter- 

 missions, at least we shall occasionally be unable to hear it where we have 

 already heard it a short time before, and where we shall shortly again recog- 

 nize it. According to my experience, it will be most frequently heard about 

 the situation of the Fallopian tube of the right side ; but it may be detected in 

 any of the lateral or anterior parts of the uterus." That the cause of this 

 sound exists in the Uterus itself, is distinctly proved by the fact, that it has 

 been heard when that organ was so completely anteverted, that the fundus 



* A plan of Dr. Reid's idea of this structure is shown in Fig. 24, (Plate I.) 

 f That the Placenta is not absolutely necessary to the nutrition of the Human foetus, any 

 more than to that of the non-placental Mammalia, is a doctrine that has been maintained 

 by several physiologists of eminence; in consequence of the not very unfrequent occur- 

 rence of cases, in which it has been very imperfectly formed, so as to be manifestly 

 unfit, at least in great degree, for the performance of its functions : and it cannot but be 

 admitted that there is much evidence in support of this view. In those cases, however, 

 in which the Placenta has been from the first imperfectly formed, the nutrition of the 

 foetus has manifestly suffered; whilst in those in which a degeneration of its structure 

 has taken place (as by the deposition of calcareous matter), there is no evidence that, up 

 to a late period of pregnancy, the foetus may not have been nourished through its means. 

 For a collection of such cases, see Dr. Dunglison's Physiology, vol. ii. [p. 448]. 

 t Op. cit. p. 121. 



