398 FKANKLIN P. MALL 



t^ese are known respectively as crown-rump {CR) and crown- 

 heel (CH). Tables were prepared by which the average measure- 

 ments of the' one for a given stage could be converted into the 

 average measurements of the other; for it is well known that 

 embryologists are given to using the crown-rump measurement 

 for smaller specimens, while anthropologists and obstetricians 

 generally use the crown-heel measurement for larger specimens. 



MENSTRUATION AGE 



My tabulation of the menstrual age was made as follows: 

 All the measurements of the embryos and fetuses were converted 

 into crown-rump or sitting-height measurements. These were 

 then used as ordinates, while the menstrual ages were used as 

 abscissae; in other words, each specimen was entered upon a 

 chart in which the menstrual age and the vsitting-height together 

 made a co-ordinate. In this way the 1000 specimens were 

 spread over a millimeter chart, 500 mm. high and 350 mm. wide. 

 It was found that the individual records arranged themselves 

 along a path about 20 mm. wide at the base line, and about 40 

 mm. wide toward the upper margin of the chart. In addition 

 to this central zone containing most of the records there were 

 numerous scattered entries far out of line. These were especially 

 numerous at the bottom of the chart, which would indicate that 

 in early abortions there is an undue number of poor records ; or, 

 at least, records showing greater irregularity in the menstrual 

 periods. In order to determine a mean menstrual age the chart 

 was marked square by square in such a way that exactly one- 

 half of the records were circumscribed by two lines enclosing the 

 usual or normal cases, leaving one quarter of the scattered records 

 to tlje right of one line, the other quarter to the left of the other 

 line. The first group includes those specimens which grew very 

 slowly and may have been pathological; the second, those cases 

 in which menstruation continued after pregnancy. The two 

 lines which include the middle group are practically parallel, 

 beginning about 20 mm. apart, around the records of the early 

 specimens, and ending about 40 or 50 mm. apart around the 

 specimens from the latter part of pregnancy. The distance 



