THE DEVELOPMENT OF THE MUSCULAR SYSTEM. 



297 



Spinal ganglion 



Dorsal musculature 



Ventro-lateral 

 musculature 



Vertebral arch 

 Dorsal ramus of 

 spinal nerve 



Scgmental artery 



Costal process 



Lat. branch of 

 nal nerve 



Vent, branch of 

 ipinal nerve 



FIG. 263. Diagrammatic cross section through the 5th-6th thoracic segments of a human embryo 

 of 9 mm. (4^ weeks). Bardeen and Lewis. 



FIG. 264. Drawing from a reconstruction of the region of the lower extremity of a human embryo 

 of 9 mm. (4% weeks). Bardeen and Lewis. 



The visceral organs and the greater part of the left body wall have been removed. The 8th thoracic 

 to the 5th sacral segments are shown. On the right side of the body the costal processes, 

 the spinal nerves (including the lumbo-sacral plexus), and the lower extremity are shown. 

 On the left side the costal processes, the spinal nerves, and the nth and i2th thoracic myo- 

 tomes are represented. Note the dorsal, lateral, and sympathetic branches of the spinal 

 nerves. 



