THE NERVOUS SYSTEM 



3S9 



Development of Sensory Nerves. While the neurites of cranio-spinal 

 motor nerves are formed as outgrowths of neuroblastic cells located in 



C NODOSUM\ 

 C PETHOSUM- 

 OTIC C 



/ACCESSORY NERVE 



i;;;7CERVICAL GANGLIA 

 /AORTA 



Fig. 344. — The autonomic system of a 16 mm. human embryo. The sympathetic 

 trunk is shown in solid black. The intestine is stippled. (Redrawn from Bremer, 

 after Streeter.) 



SPINAL CORD 

 DERMATOME 

 SOMATIC MOTOR NERVE 

 MYOTOME 



ENTERON 



SYMPATHETIC 

 GANGLION 



PRIMITIVE DUCT- 

 COELOM 



SENSORY GANGUON 



NOTOCHORD 



HYPOCHORDA 

 "DORSAL AORTA 



POSTCARDINAL VEIN 



SPINAL NERVE 



VITELUNE 

 VEIN 



MESENCHYME 



Fig. 345.- — A cross section of a 1 7 mm. cla^mobranch (Squalus) embryo, in the 

 trunk region, showing an early stage in the formation of sympathetic ganglia. The 

 yolk-sac to which the embryo is attached has been removed. 



the wall of the central nervous system, those of the sensory nerves are 

 formed as processes of ganglion cells located in the sensory ganglia. 



