Charles Eussell Bardeen and Warren Harmon Lewis 7 



The medio-lateral flattening of the distal portion of the arm-bud is 

 especially well marked. Proximal to this flattened portion swellings on 

 both medial and lateral surfaces indicate -where pre-muscle tissue is 

 developed. A constriction may likewise be seen dividing the leg-bud 

 into two distinct divisions. Owing to a slight torsion the lower portion 

 o± the leg-bud presents to view the anterior margin instead of the flat- 

 tened lateral surface. 



Fig. 9. 



X about 5 d. 



Fig. 10. 



Embryo Bi\. 

 In Fig. 9 is represented the His embryo Br,; length, 11 mm.; age, 

 about 4^ weeks. Thirty-five myotomes are pictured (8c, 12t, 51, 5s' 5c).' 

 The base of the arm lies opposite the 4th to 8th cervical and' 1st thoracic 

 spinal ganglia. The division of the arm into its main segments is 

 advanced beyond that pictured in Embryo CLXIII. The upper arm 

 still projects caudally. The lower arm, owing to flexion at the elbow 

 projects caudo-ventrally. The hand is flattened and can be distinguished 

 from the forearm. Swellings of the digits are visible. The flrst indica- 

 tions of the shoulder are present. The posterior limb shows a differen- 

 tiation of foot, leg and thigh regions. 



Embnjo CIX. 

 Fig. 10 represents Embryo CIX; length, 11 mm.; age, about 5 weeks 

 Two photographs of this embryo are reproduced in Plate I. The base 



"Externally visible segmentation at this stage is due to the spinal ganglia not to 

 myotomes. The latter have lost their identity. 



