UTERINE MILK. 875 



Functions. The placenta is the nutritive, excretory, and respiratory organ of 

 the foetus ( 368) ; the latter receives its necessary pabulum by endosmosis from 

 the maternal sinuses through the coverings and vascular wall of the villi in which 

 the foetal blood circulates. [The placenta also contains glycogen.] 



[Structure. A piece of fresh placenta teased in normal saline solution, shows the villi pro- 

 vided with lateral offshoots, and consisting of a connective-tissue framework, containing a 

 capillary network with arteries and veins, while the villi themselves are covered by a layer of 

 somewhat cubical epithelium (fig. 669).] 



Uterine Milk. Between the villi of the placenta there is a clear fluid, which 

 contains numerous small, albuminous globules, and this fluid, which is abundant 

 in the cow, is spoken of as the uterine milk. It seems to be formed by the breaking 

 up of the decidual cells. It has been supposed to be nutritive in function. [The 

 maternal placenta, therefore, seems to be a secreting structure, while the foetal part 

 has an absorbing function. The uterine milk has been analysed by Gamgee, who 

 found that it contained fatty, albuminous, and saline constituents, while sugar and 

 casein were absent] 



The investigations of "Walter show, that after poisoning pregnant animals with strychnin, 

 morphia, veratrin, curara, and ergotin, these substances are not found in the foetus, although 

 many other chemical substances pass into it. 



[Savory found that strychnin injected into a foetus in utero caused tetanic convulsions in the 

 mother (bitch), while syphilis may be communicated from the father to the mother through the 

 medium of the foetus {Hutchinson). A. Harvey's record of observations on the crossing of breeds 

 of animals chiefly of horses and allied species show that materials can pass from the foetus to 

 the mother.] 



On looking at a placenta, it is seen that its villi are distributed on large areas separated from 

 each other by depressions. This complex arrangement might be compared with the cotyledons 

 of some animals. 



The position of the placenta is, as a rule, on the anterior or posterior wall of the uterus, more 

 rarely on the fundus uteri, or laterally from the opening of the Fallopian tube, or over the 

 internal orifice of the cervix, the last constituting the condition of placenta praevia, which is 

 a very dangerous form of placental insertion, as the placenta has to be ruptured before birth 

 can take place, so that the mother often dies from haemorrhage. The umbilical cord may be 

 inserted in the centre of the placenta (insertio centralis), or more towards the margin (ins. 

 marginalis), or the chord may be fixed to the chorion laeve. Sometimes, though rarely, there 

 are small subsidiary placentae (pi. snccenturiata), in addition to the large one. When the 

 placenta consists of two halves, it is called duplex or bipartite, a condition said by Hyrtl to be 

 constant in the apes of the old world. 



Structure of the Cord. The umbilical cord (48 to 60 cm. [20 to 24 inches] long, 

 11 to 13 mm. thick) is covered by a sheath from the amnion. The blood-vessels 

 make about forty spiral turns, and they begin to appear about the 2nd month. 

 [The cause of the twisting is not well understood, but Virchow has shown that 

 capillaries pass from the skin for a short distance on the cord, and they do so 

 uuequally, and it may be that this may aid in the production of the torsion.] It 

 contains two strongly muscular and contractile arteries, and one umbilical vein. 

 The two arteries anastomose in the placenta (Hyrtl). In addition, the cord contains 

 the continuation of the urachus, the hypoblastic portion of the allantois (fig. 665, 

 VIII, a), which remains until the 2nd month, but afterwards is much shrivelled. 

 The omphalo-mesenteric duct of the umbilical vesicle (N) is reduced to a thread- 

 like stalk (fig. 665, VIII, D). Wharton's jelly surrounds the umbilical blood- 

 vessels. Wharton's jelly is a gelatinous-like connective-tissue, consisting of 

 branched corpuscles, lymphoid cells, some connective-tissue fibrils, and even elastic 

 fibres. It yields mucin. It is traversed by numerous juice-canals lined by endo- 

 thelial cells, but other blood- and lymphatic-vessels are absent. Nerves occur 

 3-8.-1 1 cm. from the umbilicus (Schott, Valentin). 



The foetal circulation, which is established after the development of the 

 allantois, has the following course (fig. 670) : The blood of the foetus passes from 

 the hypogastric arteries through the two umbilical arteries, through the umbilical 

 cord to the placenta, where the arteries split up into capillaries. The blood is 



