CHAPTER VII. 



THE OCCURRENCE OF LOCALIZED ANOMALIES IN HUMAN 



EMBRYOS AND FETUSES. 



In a paper on the causes underlying the origin of human monsters (Mall, 

 1908), I made the assertion that localized anomalies were more common in embryos 

 obtained from abortions than in full-term fetuses, without, however, adducing 

 conclusive evidence in support of this theory. 



In a footnote on page 27 of that publication I gave a list of embryos with then- 

 chief defects, comparing them with the percentage of frequency of monsters 

 born at term. Objection might be raised to such a statement on the ground that 

 there is not a complete correspondence between anomalies in the embryo and 

 those found in the fetus at the end of pregnancy. For instance, spina bifida in 

 young embryos is always complete, while at full term the open canal is covered 

 over with skin. Cyclopia and exomphaly are the same in the embryo as at birth, 

 but the deformities of the head and neck of the embryo are of such a nature that 

 it can not survive long enough to admit of comparison with similar malformations 

 found at term. With these difficulties clearly before me, I have made an effort to 

 sharply define the anomalies in embryos, so that a satisfactory comparison might 

 be made with those found in monsters at the end of pregnancy, as described in the 

 literature. 



Cyclopia is, perhaps, the type of anomaly which is now best understood, due 

 largely to the excellent experimental work of Stockard, and also partly to the fact 

 that the cyclopean state can exist quite independently of other marked deformities. 

 I have already discussed the question of cyclopia in a separate publication (Mall, 

 19l7 a ), and it is not therefore necessary for me to dilate further upon it at present. 

 Hare-lip is also sharply defined in the embryo and is as readily distinguished as 

 exomphaly. Other anomalies, however, are more difficult to recognize in the 

 embryo as sharply defined malformations. 



The pathological specimens of the first 400 accessions to our collection were 

 reported in my paper on the origin of human monsters mentioned above. Since the 

 embryological collection has been taken over by the Carnegie Institution of Wash- 

 ington it has grown at a very rapid rate, about 400 specimens being added to it 

 each year. At present, however, only the first 1,000 will be considered, the re- 

 mainder not having been sufficiently tabulated to be of statistical value. The 

 specimens can clearly be divided into two groups according to their origin, i. e., 

 uterine and ectopic. In both of these the embryos which are normal in form are 

 catalogued according to then- sitting height, which we call crown-rump (CR). The 

 chief difficulty, however, is to determine what constitutes a normal embryo, and 

 here we must rely largely upon our experience in human and comparative embry- 

 ology. A sharply defined, well-formed, white embryo, with blood-vessels shining 

 through its transparent tissues, is considered normal. If it is partly stunted and 

 opaque or disintegrating it is considered pathological. A further study of the 



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