86 OBSTETRICAL PHYSIOLOGY. 



texture, better organization, greater extent, and more persistent character 

 of their " deciduous " formations. 



The comparative study of the disposition of the different kinds of 

 placentae, may furnish valuable indications as to the procedure which 

 ought to be adopted in artificial delivery ; the surgical manipulation 

 necessarily varying with the extent and arrangement of the points of 

 union existing between the uterus and the foetal envelopes. 



It has, therefore, been thought useful to arrange the domesticated 

 animals into two groups ; those with a single placenta, and others with a 

 multiple placenta ; the first group being again subdivided according as 

 the placenta is " diffused " or " localized." This arrangement and subdi- 

 vision may be expressed as follows : — 



Single Placenta 

 Multiple Placenta 



Diffused 



Horse. 

 Pig. 

 Cow. 

 Localized -^ Sheep. 

 Goat. 



S 



Zonular 



Dog. 

 Cat. 



UiTBiLicAL Cord. 



The umbilical cord^ funis ^ or navel-string, is a collection of vessels which 

 forms the means of communication between the mother and foetus, during 

 the uterine existence of the latter, and which loses its functions when 

 birth occurs. It is visible at the earliest period of pregnancy, and is 

 formed by the vessels which convey the blood between the foetus and its 

 envelopes — chiefly the placenta. It is divided, for facility of description, 

 into two portions : an amniotic, the longest, always twisted on itself like 

 a rope, and covered by the amnion, which passes along it to become con- 

 tinuous with the skin at the umbilicus ; and an allantoic portion, much 

 shorter, less twisted, and covered by the sheath that continues the two 

 layers of the allantois until it is inserted into the upper wall of the chorial 

 sac, between the two cornua. 



Three vessels enter into the composition of the cord : two arteries and 

 a vein, which are embedded in embryonic connective tissue ( Whartonian 

 gelatine^ that makes them appear more voluminous than they really are. 

 This " Gelatine of Wharton " consists of a mucus basis, in the substance 

 of which is fibrillar tissue. The umbilical arteries arise from the internal 

 iliac artery, and pass along the sides of the bladder ; reaching the umbil- 

 icufs, they pass through it and arrive at the terminal extremity of the 

 amniotic portion of the cord, where they give off some branches to the 

 amniotic sac, and then continue to the end of the allantoic portion, where 

 they terminate by an expansion of placental branches. The amniotic 

 divisiojis of these arteries are extremely flexuous and few in number ; 

 they are included between the allantoic layer and the membrane of the 

 amniotic sac, within which they are prominent. 



The placental or chorial divisions are infinitely more numerous and 

 larger, and starting from the terminal extremity of the cord, pass in every 

 direction bftween the chorion and the external layer of the allantois, 

 beneath which they can be seen. By their anastomoses they form a 

 beautiful network, whence proceed the capillary vessels that form the 



