THE UMBILICAL CORD. 9S; 



Functions. 



The functions of the placenta are obvious : it is the nutrient and 

 respiratory apparatus durin<^ a portion of intra-uterine existence ; and 

 for the acconiphshment of these functions it must rely upon its intimate 

 and healthy relations with the uterine surface. The special and tempo- 

 rary processes of development being completed, and the task of provid- 

 ing capillary superficies being terminated, whether on the part of the 

 mother or foetus, the placenta of the latter disappears, as well as the 

 decidua ; though they may not be thrown oil' together, and the maternal 

 decidua may not be shed all at once, but in successive portions. The 

 long period of gestation necessary to endue the young of defenceless- 

 hoofed animals with suthcient strength before birth, is perhaps a reason 

 for the firmer texture, better organisation, greater extent, and more 

 persistent character of their " deciduous " formations. 



The comparative study of the disposition of the different kinds of 

 placenta?, 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 fa^tal 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 " localised." This arrangement and sub- 

 division may be expressed as follows : — 



Single Placenta 



Multiple Placenta 



Diffused 

 Zonular 



Horse. 

 Pig. 

 Dog. 

 Cat. 

 j Cow. 

 Localised • Sheep. 



( Goat. 



U.MIilLICAL CouD. 



The umbilical cord, funis, or navcl-strimj, is a collection of vessels 

 which form the means of connnunication 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 fuutus 

 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 continuous with the skin at the umbilicus ; and an allantoic 

 portion, much shorter, less twisted, and covered by the sheath that con- 

 tinues the two layers of the allantois until it is inserted into the upper 

 wall of the chorial sac, between the cornua. 



Three vessels enter into the composition of the cord : two arteries a.nd 

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

 gelatine), ih^t make them appear more voluminous than they really are. 

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

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

 ternal iliac artery, and course along the sides of the bladder ; reaching 

 the umbilicus, they pass through it and arrive at the terminal extremity 

 of the amniotic|)ortion of the cord, where they give off some branches 



