ON THE FATE OF THE MUSCLE-PLATE. 121 



Fig. 9. a. Longitudinal section through the body of a Chick embryo 

 aged four days six hours, in the region of the fore limb, 

 cutting through the body wall (B. W.) just below the level 

 of the muscle-plate. The body cavity (B.C.) is seen, and in 

 the body wall are the three nerves (N., 1, 2, 3), and the artery 

 (art.) going to the limb. b. This section is made farther out 

 at the root of the limb bud, and shows the thickening of 

 the body wall, with the formation of the plexus, around 

 the artery (art.). The vein (v.) is also seen. The nerves 

 in the plexus are here on the point of separating into two 

 bundles, c. From a section made still farther out in the 

 limb. The nerves, after forming the plexus, have more 

 completely separated into a dorsal and a ventral bundle 

 (d. and v.), with the artery in the middle, d. Here the 

 limb bud is more apparent; it is becoming separated from 

 the body wall ; and the dorsal and ventral bands of nerve 

 are well defined in the blastema. 



Fig. 10. From a longitudinal section through the body of the same 

 embryo in the region of the hind limb (H.L.), to show 

 the lateral division and union of the dorsal and ventral 

 divisions of the nerves to form the plexus (plex.). The 

 spinal cord (Sp. C.) and spinal ganglia (Sp. g.) are also 

 shown. 



Fig. 11. Transverse section through trunk of Chick embryo aged 

 four days twelve hours, between the limbs, to show the 

 muscle-plate and the spinal nerve. The division of the 

 latter into its two terminal branches (/. i.) is seen. 



Fig. 12. Transverse section through the same embryo, in the region 

 of the fore limb. The spinal nerve is seen dividing at 

 the root of the limb into dorsal (d.) and ventral (v.) 

 branches. These enclose and are surrounded by masses 

 of formative blastema (1, 2, 3), the precursors of the 

 muscles and skeleton of the limb. The muscle-plate 

 (rn. p.) occupies its original position. 



Fig. 13. Transverse section through the trunk, between tho limbs, 

 of an embryo aged five d;iys, to show the relative position 

 and growth of the muscle-pktc (m. p.) and nerve (N.). 



