ON THE FATE OF THE MUSCLE-PLATE. 129 



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 (m. p.) occupies its original position. 



Fig. 13. — Transverse section through the trunk (between the limbs) of an 

 embryo aged five days, to show the relative position and growth of the 

 muscle-plate (m.p.) and nerve (N.). 



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. 

 d. and v. Dorsal and ventral divisions. 3. Commencing formation of carti- 

 lage 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 (2V. 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 (J.) primary divisions of a spinal nerve from a Rat embryo. Sp. C. 

 Spinal cord. Sp. G. Spinal ganglion. No. Notochord. Ao. Aorta. 



VOL. XXVIII, PART 1. NEW SER. 



