412 FOETAL DYSTOKIA- 



maticMis, is to the effect that the embryo or fcetus has been submitted to 

 some kind of alteration in uiero, and that this has been produced during 

 the interval between conception and birth. It is a matter of ordinary- 

 observation that sometimes a fall, blow, sudden fright, or a' powerful 

 mental impression will, in woman, disturlD the ordinary course of preg- 

 nancy, and give rise to more or less unusual symptoms, and even prema- 

 ture birth of an imperfect fcetus. It has been attempted to explain the 

 action of these influences, by supposing that the sudden physical or men- 

 tal shock produces an abrupt contraction of the vascular system and, co- 

 incidentally, of the uterus ; and that the foetal membranes are thus all 

 at once constricted, and slightly lacerated. Consequently, a part of the 

 liquor amnii escapes (as has been frequently observed), and this is suc- 

 ceeded by adhesion of the margin of the laceration in the membranes to 

 the corresponding part of the body of the embryo ; and thus are formed 

 those layers or bands which, whether temporary or permanent, disturb 



Fig. 102. 

 Double Parasitic Monstrosity; Polytnelian notomelus ; Cow. 



more or less the development of the young creature, either by prevent- 

 ing organs from occupying their natural cavities, hindering the union or 

 fusion of parts, or opposing or delaying the formation of those which 

 should afterwards appear. That this opinion is not improbable may be 

 at once conceded, when we remember that during the early stages of 

 development the ovum is little more than a semi-fluid mass, and that its 

 constituent parts are extremely impressionable. 



But the formation of mcxistrosities is more particularly due to what has 

 been designated the theory of retardation or arrested development ; the de- 

 viations from the normal standard being the effect of disturbance and 

 arrested supply of nutriment during the period of intra-uterine growth. 

 G. Saint-Hilaire has proved experimentally, by means of eggs artificially 

 hatched, that the production of monstrosities is due to the interruption 

 or accidental suspension of development which had commenced in a 

 regular manner; while Meckel has shown the striking analogy there ex- 



