122 A. M. PATERSON. 



Fig. 14. Transverse section through the trunk and root of the fore 

 limb of an embryo of the same age. m. p. Muscle-plate. 

 N. Spinal nerve, cl. and v. dorsal and ventral divisions. 

 3. Commencing formation of cartilage in centre of limb, 

 with a layer of dense blastema surrounding it. 2 and 1. 

 Commencing formation of muscles above and below the 

 nerve-trunks, art. Axillary artery, v. Axillary vein. 



Fig. 15. Successive longitudinal sections through the root of the 

 fore limb of a Chick embryo aged five days twelve hours. 

 The defined borders represent the body cavity. From a. 

 to e. the nerves {N., 1, 2, 3) are seen to divide into dorsal 

 and ventral branches (d. v.), which unite laterally to pro- 

 duce secondary dorsal and ventral trunks. Art. and v. 

 Axillary artery and vein. 



Fig. 16. Diagram to illustrate the formation of the superior (S.) and 

 inferior (/.) primary divisions of a spinal nerve from a 

 Rat embryo. Sp. C. Spinal cord. Sp. g. Spinal ganglion. 

 No. Notochord. Ao. Aorta. 



