A HUMAN EMBRYO BEFORE THE APPEARANCE OF THE MYOTOMES, 



BY N. WILLIAM INGALLS. 



The specimen which forms the subject of this paper came into my possession 

 some time ago through the kindness of Dr. E. Peterka, of Cleveland. In the 

 collections of embryology and teratology of the Department of Anatomy of West- 

 ern Reserve University it is listed as embryo No. 1. On account of the very 

 interesting and important stage of human development which it illustrates, a 

 detailed investigation of its more essential features, especially as regards the 

 embryo proper, has been undertaken. The extra-embryonic structures, chorion, 

 body-stalk, and yolk-sac, and the evidence they offer on early blood and blood- 

 vessel formation, will not be dealt with in detail at this time. 



The intact ovum, when it came into my hands, had been for about a month in 

 alcohol of unknown strength, but was, on account of its small size, quite well pre- 

 served. The following brief history accompanied the specimen: 



April 2. Intercourse (also about two weeks before?). 

 April 8. Period expected; regular 24 to 26 days. 

 April 14. Bleeding commenced, gradually increasing. 

 April 17. Ovum cast off. 



Before entering upon a discussion of the anatomical findings, something may 

 be said as to the probable age of the specimen. Following the example of Bryce and 

 Teacher (1908), which has been adopted so frequently, one can set up a similar 

 table for the embryo in question : 



The estimated age of 17 to 18 days was put in parenthesis in the above table 

 because we could not bring ourselves to look upon it with any very great degree of 

 confidence. The figures were obtained by comparison with embryos which were 

 obviously in a stage of development either more or less advanced and by reference 

 to the recent estimates of Triepel (1914) and Grosser (1914). Triepel's suggestion 

 of subtracting about 18 days from 34 in this case would give an age of about 16 days. 

 Embryo No. 1 is far in advance of both that described by Fetzer (1910) and the v. 

 Herff embryo of Graf Spee (1896), the ages of which have been given as 15 and 17 to 

 18 days respectively. On the other hand, it is distinctly less advanced than Frassi's 



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