XII. 24 



BRAIN 



345 



synaptic connexions are made in a complicated 'neuropil' (Fig. 201). 

 This is a simpler arrangement than is found within the grey matter of 

 the mammalian curd. 



n.otf. 



cer.h. 



cereb. 



n. 9, 10,11 



Fig. 203. The brain of Rana, dorsal view. 



cer.h. cerebral hemisphere; cereb. cerebellum; epi. epiphysis; hth. hypothalamus; hyp. pitui- 

 tary gland; lam.t. lamina terminalis; olf.l. olfactory lobe; n.olf. olfactory nerve; n. 3-1 1 cranial 

 nerves; «. (1 and 2), spinal nerves; opt. c. optic chiasma; opt.l. optic lobe; opt.t. optic tract. 

 (Modified from Gaupp.) 



The arrangement of the spinal nerves is much modified by the 

 development of the limbs. Ten spinal nerves are found but since an 

 embryonic first one is missing they are sometimes numbered 2-1 1 (Fig. 

 202). Two spinal segments contribute to the brachial and four to the 

 sciatic plexuses in the frog. From these plexuses fibres are distributed 

 to the muscles and skin of the limbs (Fig. 202). 



