A circumvolution of this kind may some times become dangerous : 1. By acting as a ligature round the neck, and producing stran gulation of the foetus (Buchanan, Hebenstreit) ; 2. By constricting one of the extremities, and producing the spontaneous amputation of Montgomery (Art. Fcurns,fig. 157. Vol. IL) 3. By forming single or compound knots. Although these are in general not dangerous, while the vessels are sufficiently protected against pressure by the Whartonian gelatine, they may nevertheless in some cases be drawn so tight as to obstruct the communication between mother and child (Sandifort, Irvets, D. W. H. Busch) ; and sometimes the um bilical cord breaks off near the knot when the vessels have become obliterated by the pres sure. Fig. 598. gives an example of this in an acephalus.
5. The umbilical cord too short. —Wrisberg gives as a minimum a measure of seven inches. It may, however, be much less. This short ness of the cord is in general accompanied by a deformity of the fetus, usually by eclopia of the abdominal viscera, by which it indi dicates an arrest of developement at an earlier period of embryogenesis. In this way we
should interpret the accounts of absence Of the umbilical cord.
6. Absence of one of the umbilical arteries, is even observed in double monsters, but occurs principally in eclopia viscerunz abdonzi naliunz, and in defective formation of the infe rior part of the body. Serres hence derived the conclusion, that this malformation is the con sequence of the want of one of the umbi lical arteries ; which is however wrong, as the evolution of the whole body may be complete, even when one of the umbilical arteries is wanting. .7%)..599. represents a specimen of this kind.
recorded cases, the superior extremities were wanting, and the anus was closed. In other cases it is occasioned by an enormous quan tity of the liquor amnii, which is usually accompanied with an abnormal developement or impeded growth of the fcetus.