128 A. M. PATEESON. 



EXPLANATION OF PLATES VII & VIII, 



Illustrating Dr. Paterson's paper " On the Fate of the 

 Muscle-Plate, and the Development of the Spinal Nerves 

 and Limb Plexuses in Birds and Mammals." 



Fig. 1. — Semi-diagrammatic view of transverse section through the trunk 

 of a Chick embryo at the end of the third day. Both spinal nerve (N.), with 

 its roots and ganglion (Sp. g.) and muscle-plate (m.p.) are shown. The spinal 

 cord, notochord (No.), aorta (Ao.), and cardinal vein (C. V.), are also indicated. 

 The muscle-plate is just entering the body wall. The section is taken between 

 the limbs. 



Fig. 2. — View showing same structures in an embryo of three days in the 

 region of the fore limb. 



Fig. 3. — From an embryo of three days six hours old, showing the growth 

 of the muscle-plate {m.p.) and spinal nerve (N.) in the trunk between the 

 limbs. 



Fig. 4. — From the same embryo in the region of the fore limb. 



Fig. 5. — From an embryo aged three days fifteen hours, showing the further 

 growth of the muscle-plate (m.p.) and nerve (N.) in the trunk between the 

 limbs. 



Fig. 6. — Shows the same structures in the region of the fore limb. 



Fig. 7. — From an embryo aged four days, with the muscle-plate presenting 

 growing points at the two ends, and the nerve dividing in the body wall int 

 a ragged bundle. The formation of the superior primary division (*.) of the 

 nerve and the cord to join the sympathetic (sy.) are also seen. 



Fig. 8. — From the same embryo, through the fore limb, showing the relative 

 position of the muscle-plate and nerve. The nerve is seen dividing in the limb 

 into a sheaf of branches. 



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 stili 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 



