48 MAX MAYO MILLER 



per cent. This indicates that during this period the growth along 

 the longitudinal axis is greater than in the transverse diameters. 

 The 65 mm. embryo in cross-sectional area shows a small absolute 

 decrease over the 31 mm. embryo in the cervical region. This 

 decrease is probably due to individual variation. During the 

 latter part of the first half of prenatal life the relative growth in 

 area of cross-section continues relatively less than the growth in 

 volume, as compared with the younger stages. By using the 

 areas of the cross-sections of the 5th cervical segment as given by 

 Donaldson and Davis ('03) (taken from StiUing) for a child of 

 two years and a composite adult, an increase of 600 per cent occurs 

 in the child, as compared with the 150 mm. embryo and of only 

 100 per cent between the child and the adult. 



b. Thoracic region. The thoracic region in volume shows an 

 increase of slightly less than 400 per cent between the 11 mm. 

 embryo and the 65 mm. specimen. This is more than the in- 

 crease in the cervical region during the same time, which is less 

 than 300 per cent. x\s a result, the thoracic region, which is 

 smaller than the cervical region in the 11 mm. embryo surpasses 

 it in the 17 mm. embryo. From the 65 rmn. embryo to the mid- 

 fetal period (150 mm.), the thoracic continues to increase slightly 

 more rapidly than the cervical region. This is also true for the 

 thoracic region when compared with the cord as a whole, as 

 shown in table 1. The thoracic region of the cord continues to 

 increase relatively through postnatal life, forming 50 per cent 

 of the adult cord, while the cervical forms only 31 per cent. 



In cross-sectional area the thoracic segments from the 3rd to 

 the 8th are practically constant. The relatively slight increase 

 in cross-sectional area from the 17 mm. to the 65 mm. specimens 

 (tables 3 to 5) is in agreement with the previous statement that 

 during this period the growth is greatest along the longitudinal 

 axis. The cord of the 31 mm. embryo is even slightly smaller 

 in cross-sectional area than that of the 17 mm. embryo in the 

 thoracic region. This absolute decrease is probably due to an 

 individual variation. By using data for the child and adult, 

 taken from Donaldson and Davis ('03) and Stilling ('59) it is 

 shown that in the time which elapses between the mid-fetal 



