PLATE 9 



EXPLANATION OF FIGURES 



28 Transverse section passing through the dorsal root and ramus ventralis 

 from an adult Amphioxus. Note the ganglion cells scattered through the dorsal 

 root, ramus ventralis and dorso-lateral portion of the spinal cord. X 50. 



29 Graphic reconstruction of two spinal nerves from an adult Amphioxus. 

 Observe that the motor and sensory components are widely separated and that 

 the ganglion cells are scattered through the sensory rami and the dorsal root. 

 The light area immediately outside the motor rami, bordered by a dotted line, 

 I take to be fibrous connective tissue. X 50. 



30 Diagrammatic transverse section of the motor and sensory components 

 of a spinal nerve of one of the higher vertebrates. 



31 Graphic reconstruction of an abdominal spinal nerve from a 6 mm. pigeon. 

 Observe the presence of rami ventrales, which have the appearance at first sight 

 of being mixed nerves, but which upon closer examination of their finer structure 

 are shown to have separate motor and sensory bundles running side by side. 

 X 50. 



32 Graphic reconstruction of two abdominal spinal nerves from an 8 mm. 

 pigeon embryo. Note the presence of short rami dorsales. Both the rami 

 dorsales and rami ventrales have the appearance of being mixed nerves, but an 

 examination of their finer structure shows the motor and sensory fibers of the 

 rami dorsales to be separate throughout and the motor and sensory fibers of the 

 rami ventrales do not intermingle before the level of the aorta is reached. X 25. 



33 Abdominal transverse section of a 10 mm. turtle embryo passing through 

 the ramus ventralis of a spinal nerve. Observe the difference in structure of 

 the motor and sensory components. X 50. 



34 Transverse section of a 19 mm. Squalus acanthias embryo, showing the 

 point of union of the motor and sensory nerves to form a mixed ramus ventralis 

 a little below the vertebral sympathetic ganglion. X 163. 



35 Shows the general appearance of the motor and sensory portions of the 

 ramus ventralis at the level of the aorta in a transverse section through the abdo- 

 men of a 19 mm. Squalus acanthias embryo. Note that the motor and sensory 

 fibers are separated by a layer of connective tissue or neurolemma cells. X 163. 



ABBREVIATIONS 



a., inner border of myotomes R.D.S., ramus dorsalis or posterior 



Ao., aorta (sensory) 



b., outer border of myotomes R.V., ramus ventralis or anterior 



C.T., connective tissue or neurolemma jiv.M., ramus ventralis or anterior 



cells? (motor) 



D.R., dorsal root (radix posterior) r. t^ a ^ i- + ; 



,, ' ^ * R.V.S., ramus ventralis or anterior 



Myo., myotomes , . 



Nc, notochord 



N.C., nerve cell '"^P'^^-' ^P^^^^ ''^^^ 



R.C., ramus communicans '^p.G., spinal ganglion 



R.D., ramus dorsalis or posterior Sy.G., sympathetic ganglion 



R.D.M., ramus dorsalis or posterior V.R., ventral root (radix anterior) 

 (motor) 



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