154 OBSTETRICAL PHYSIOLOdY. 



the occurrence of twins, triplets, or even more young creatures at a 

 birth, is not so rare. 



The causes of muUiparity are not well ascertained. It may be due 

 to simultaneous ripening of two or more Graafian vesicles, which, 

 rupturing at the same time, allow the escape of the ova they contain, 

 and which may become impregnated at a single coitus. Or a Graafian 

 vesicle may contain two or more ova, as Bischoff has witnessed in 

 w^oman ; and these arriving together in the uterus, may be fecundated 

 at one time. Or it may even happen that the vitelline membrane con- 

 tains two yolks, as sometimes occurs in the fowl's egg ; and as the 

 vitelline mass is the essential part of the egg, it is evident that when 

 this contains two of these masses, they ought, if fecundated, to produce 

 two embryos. 



In the first case, each foetus has ordinarily all its appendages dis- 

 tinct and completely independent ; or it may be that the two chorions 

 are fused together, in which circumstance the two foetuses will then 

 have a common envelope. In the second hypothesis, this fusion of 

 the chorions appears to be the rule, although the envelopes may also 

 be independent ; and in the third case — that of the two vitelluses 

 contained in the same vitelline membrane — not only the envelopes, but 

 also the foetuses may become united more or less closely, and thus give 

 rise to double monsters. 



Finally, it is also possible that two ova may become^ detached from the 

 ovarian cluster, though not simultaneously, but successively ; and be 

 fecundated, one after another, at two consecutive copulations within a 

 brief period. Occurrences of this kind, by no means rare, have been 

 wrongly adduced as instances of superfoetation. 



Mare. 



Of all the domestic animals, the Mare is the one which least frequently 

 brings forth more than a single creature at a birth ; and Saint-Cyr has 

 only been able to collect fourteen instances, though we have been more 

 fortunate. Eueff admits that one case of gemellar gestation may occur 

 in this animal in every 250 normal cases, but that the young are nearly 

 always born dead or die soon after birth. In the register of a stud, only 

 one instance of twins was found in every 236f births. 



Demoussy, cited by Saint-Cyr, observed an example of double gestation ; but the 

 Foals, though alive when born, perished soon after. Lemaltre gives a similar instance ; 

 only that one of the fcEtuses was expelled at four months, while the other was retained, 

 was foaled alive at the usual time, and survived. Trelut has seen a Mare which, at the 

 tenth month of pregnancy, cast two well-formed Foals. She had been put to the stallion 

 five times— on April 23, May 4, 16, and 25, and June 5 ; she aborted on March 15. Her 

 abdomen was enormously large, and some time before abortion she had received a kick in 

 the flank. 



A fourth example of double gestation is related by Goux. The two Foals— a Colt and 

 a Filly — were alive when born, and continued to thrive. Saint-Cyr's father, an agricul- 

 turist, witnessed an analogous occurrence, the progeny also surviving ; and Saint-Cyr 

 himself saw a twin birth in a Mare, one of the Foals, which was born dead, weighing 

 25 kilogrammes ; the other, which lived, weighing nearly 2G kilogrammes. 



In the Veterinarian are found a number of instances of twin Foals in this country. 

 Mr. Milliufjton (vol. iv., p. 424) gives three cases of this kind, the Foals being born alive. 

 In vol. ix. (p. 450) an account is given of a Mare which died of hydrops uteri, in which 

 were twin Foals ; in vol. xii. (p. 288) is another account of two born dead, and in vol. xvii. 

 (p. 177) a similar instance. 



A most unusual case of twin-birth is related in the North British Afjricultiirist for 

 May 17, 1876 :— A Mare, the property of Mr. Chapman, farmer, Halnaby, gave birth to 



