PRENATAL GROWTH OF SPINAL CORD 45 



than those apparently shown on the curve, due to the curvature of 

 the cord and the corresponding obUquity of the sections. 



In the 31 mm. embryo (table 4, figs. 3 a, 3 b, and 3 c, and fig. 8) 

 the upper three segments are so cut as to contain both medulla 

 and spinal cord. The outline of the cord could be measured sepa- 

 rately, however. The cervical enlargement is recognizable also 

 in this cord. This is the youngest embryo in which there is a well- 

 marked lumbar enlargement. This does not agree with Bryce 

 ('08) who states that the cervical and lumbar enlargements are 

 only manifest at the end of the third month. However, Streeter 

 ('11) finds indications of the enlargements at the end of the fir.st 

 month, while Minot C92) states that they occur at two months 

 (well developed at three months) . The cord of the 31 mm. embryo 

 is but slightly larger in area of cross-section (and even smaller in 

 places) than that of the 17 mm. specimen. The difference may be 

 due in part to individual variation and in part to the growth being 

 chiefly along the longitudinal axis about this period. 



The upper two cervical segments in the 65 mm. embryo (table 

 5 and fig. 9) are lacking. They were estimated to complete the 

 data. This was done by assuming that these segments would 

 show the same relative increase as other segments of the same 

 cord, when compared with corresponding segments of the cord in 

 the 31 mm. specimen. They are enclosed in parentheses in the 

 table. A marked variation occurs in this cord. The cervical 

 enlargement appears relatively small. The lumbar enlargement 

 shows a greater area of cross-section than the cervical enlargement. 

 As this relation is not found in any other cord examined, it is due 

 either to more rapid relative growth of the lower portion of the 

 cord at this period or (more probably) to an individual variation. 

 The tapering of the lower extremity of the cord is completely 

 shown here, since all the lower segments were measured separately 

 in this specimen. 



In the cord at the middle of the prenatal period (150 mm.: 

 table 6 and fig 10) the upper three cervical segments are missitig. 

 These were estimated as above. This cord agrees well with the 

 general description previously given. 



