Nervous Systems 



837 



obstacles, selected small bits of food \'isiially, but paid little attention to a 

 threatening approach.'*^''* Stimulation of the striatum elicits movements of 

 the beak and other structures, and removal of lar^e parts of the striatum 

 causes severe behavior deficiencies. "*'"'•' 



The non-laminated neocortex of submammalian classes deserves more 

 study, particularly observations of electrical responses; at present it is not 

 possible to assign to it any specific function. 



The mammals present a wide range of cortical function which is well il- 

 lustrated bv the increasing complexitv of responses to electrical stimulation 



Arm 



Trunk ' 



Head 



PLATYPUS 



B 



Lateral olfactory Iract 

 Olfactory tubercle 



Rhinal fissure 



MARSUPIAL 

 (Trichosurus) 



Fig. 310. Lateral views of distribution of total excitable (motor) cortex. A, In the 

 monotreme Ornithorhynchiis, From Abbie.^ B, In the marsupial Trichosurus. From 

 Abbie.^ 



in the series from monotremes to primates. The number of discrete move- 

 ments that can be elicited on electrical stimulation is quoted as less than 10 

 in monotremes and marsupials,^" 28 in an ant-eater,'"^ and several hun- 

 dred in higher primates. The monotremes Echidna^*'^ and Tachyglosstis^ 

 have a band of motor cortex with gross representation from above downward 

 of tail, hind legs, trunk, fore-legs, and head: the motor cortex activates a 

 long corticospinal tract, there being no pyramidal tract. In Ornithorhynchus 

 (Fig. 310, A), on the other hand, a large portion of the cortex is excitable 

 with overlapping representation of fore limbs, head, and evelids, and with 

 no good representation of tail and hind limbs. In marsupials also the excit- 

 able areas are poorly defined and there is much overlap (Fig. 310, B); the 

 fore limbs and head are represented and in only one of the three marsupials 



