324 TTTF. NERVOUS SYSTEM 



spinal cord may affect only one lateral half and cause a homolateral paralysis 

 below the lesion (Fig. 241, D), it is common for both lateral halves to be involved 

 and for the resulting paralysis to be bilateral (Fig. 241, ). 



The Extrapyramidal Motor Paths. In recent years it has become increasingly evi- 

 dent that the pyramidal system is not the only channel through which volitional impulses 

 are able to reach the primary motor neurons of the brain stem and spinal cord. Rothmann 

 (1907) found that, after section of the lateral corticospinal and the rubrospinal tracts in 

 monkeys at the level of the third cervical nerve, voluntary movements were lost for a time, 

 but soon reappeared; and he concluded that there must be an extrapyramidal volitional 

 path in the ventral funiculus. Three years later Schafer (1910) showed that in monkeys 

 the paralysis, which results from section of the pyramids of the medulla oblongata, is not 

 complete and persistent; and he agreed with Rothmann that there must be some other path 

 for volitional impulses. He believes that this alternative path is formed by descending 

 fibers in the ventral funiculus and in the ventral part of the lateral funiculus, since section 

 of these fibers produces as complete and persistent paralysis in monkeys as does section of 

 the pyramids themselves. 



Sherrington and Graham Brown (1913) excised the arm area of the cerebral cortex 

 in the chimpanzee, and found that function in the corresponding limb was completely re- 

 stored in a few weeks. They were able to show that this was not attributable to the vicarious 

 activity of the corresponding postcentral or the opposite precentral cortex. Horsley's (1909) 

 patient, who recovered some degree of control over the arm after the removal of its cortical 

 center in the precentral gyrus, shows that the observations of Sherrington and Brown are at 

 least in part applicable to man. 



We know that the cerebral cortex is connected through efferent projection tracts with 

 the thalamus and red nucleus and through collaterals from the corticospinal fibers with the 

 corpus striatum (Cajal). But we do not know which, if any, of these systems of projection 

 fibers constitutes a part of the extrapyramidal path for volitional impulses. 



A great deal of attention has recently been given by clinical neurologists to the dis- 

 turbance of voluntary movement by tremor, rigidity, and athetosis, which results from lesions 

 of the corpus striatum. This body seems to contain an important motor center, and ac- 

 cording to Wilson (1912 and 1914) it exerts a steadying influence upon voluntary move- 

 ments. The globus pallidus seems to be connected with the spinal primary motor neurons 

 by way of the striorubral and rubrospinal tracts. It is also possible, especially in view 

 of the important motor functions attributed to the ventrolateral descendnig tracts of the 

 spinal cord by Rothmann and Schafer, that efferent impulses reach the spinal cord from the 

 globus pallidus by way of the substantia nigra over the strionigral, the somewhat hypothetic 

 nigroreticular, and the reticulospinal tracts. It is known that the axons arising in the sub- 

 stantia nigra run into the reticular formation of the mesencephalon, beyond which they 

 cannot be traced (Cajal, 1911). According to Collier and Buzzard (1901) the rubrospinal, 

 vestibulospinal, tectospinal, and reticulospinal tracts probably represent the original paths 

 for impulses from higher to lower parts of the nervous system; and the path from the 

 cerebrum to the spinal cord, at first indirect, has been short-circuited in the mammal 

 through the evolution of the pyramidal system. 



When it is remembered that the pyramidal system is a late development, present only 

 in mammals, it does not seem unreasonable to think that some other and older path for 

 volitional impulses may also exist. The globus pallidus, the representative of the primitive 

 corpus striatum of the lower vertebrates, has been called the paleostriatum (Elliot Smith, 

 1919). From this basal nucleus there arises in all vertebrates an important efferent bundle, 



