Warren Harmon Lewis 



151 



siderably in size. The cells which fill it resemble those in LXXVI, but 

 are more closely packed together and stain deeper. There is no differen- 

 tiation of this mesenchyma. Thin-walled blood-vessels are numerous, 

 the border vein (Eandvene of Hochstetter) is present. Numerous mito- 

 tic figures indicate that there is a rapid proliferation of the mesenchymal 

 cells. The myotomes are fairly well defined, though in places the ven- 

 tral end is not always sharp and the possibility of wandering of cells 



tj^ '" ^ I \^ ,intei\ertebral disc 

 ^-Ur- i^\i'i^^; %\ ^tlnen-ical 



bolder vein 



Fig. 4. Cross section through the eighth cervical myotome and nerve of 

 embryo LXXX. X 50 diameters. 



from it into the arm bud cannot be denied. The almost constant pres- 

 ence of several blood-vessels at the ventral end of the myotome would 

 interfere somewhat with that process. The spinal nerves have grown 

 out some distance from the cord, they however pass by the median side 

 of the myotomes without sending branches into them. The distal ends 

 of the nerves reach beyoud the myotomes. The lower four cervical and 

 first dorsal end at the root of the arm. As will be seen in Fig. 4, this 

 end of the nerve spreads out somewhat and is surrounded here as well 



