44 MAX MAYO MILLER 



relatively longer and slenderer during the prenatal life, and this 

 tendency continues in the child to the adult. 



2. Special features in the various embryos: (figs. 1 to 12; 

 tables 2 to 6) 



In the 11 mm. embryo only the cervical and thoracic segments 

 were measured separately. By referring to table 2 and figure 6, 

 one can readily see that this embryo differs somewhat from the 

 preceding general description. Owing to the obliquity of the 

 section in the cervical and lower thoracic regions (due to the 

 normal curvature of the spinal cord in embryos of this length), 

 not much stress can be laid on the apparent increase in area of 

 cross-section in these regions as shown in the curve. However, 

 from measurements of the transverse diameters (which are not 

 affected by the obliquity) of these sections, which show an 

 increase in the cervical region, the indications are that there 

 is a slight expansion in the region of the cervical enlargement. 

 There is, however, no evident lumbar enlargement. The appar- 

 ent increase shown in the curve in the lower thoracic region is 

 probably due entirely to the obliquity of the sections. Except- . 

 ing the slight cervical enlargement, the cord seems to taper from 

 the cephalic end to the caudal extremity. The lower end of the 

 cord is so curved that the segments could not be separated. The 

 shape of the cord in cross-section (figs. 1 a and 1 b) is in general 

 like that of a rectangle with the corners rounded. The outline is 

 not smooth, due probably to the fact that the columns of white 

 matter are as yet not formed. 



The spinal cord of the 17 mm. embryo presents (as shown in 

 table 3, figs. 2 a and 2 b, and fig. 7) some of the same features as 

 the cord of the 11 mm. specimen. From the increase in areas of 

 cross-section and in the transverse diameters of the sections, it is 

 evident that there is in this cord a noticeable increase in the region 

 of the cervical enlargement, and a very slight increase in the lower 

 thoracic and upper lumbar segments which is possibly due in part 

 to the beginning of the lumbar enlargement. The actual in- 

 creases both in the cervical and thoraco-lumbar regions are less 



