536 



THE NEEVOUS SYSTEM. 



The best -known long or extrinsic systems of fibres in the antero- lateral 

 funiculus are those known as the fasciculus cerebrospinalis lateralis (O.T. crossed 

 pyramidal tract), the fasciculus cerebrospinalis anterior (O.T. direct pyramidal tract), 

 the fasciculus cerebellospinalis (O.T. direct cerebellar tract) (which goes from the 

 spinal medulla to the cerebellum, and ought therefore to be called spinocerebellaris, 

 as it will le subsequently named in this account), and the fasciculus anterolateralis 

 superficial (O.T. Gowers' tract). 



There are, however, many other fasciculi at least as important as these, but 

 there is as yet no close agreement as to their precise limits or connexions. One 

 reason for this is that some of the elements of one tract may become intermingled 

 with those of another ; moreover, the position and relations of certain of them 



Optic tract 



Te'ctum mesencephali 

 I Red nucleus 



Tecto-spinal tract 



;,, ^'Rubro-spinal tract 



Metathalamus 

 Thalamusx, 



^ Brachium conjunctivum 



.-* Lemniscus medialis 



" Lemniscus lateralis 

 Cerebellum 



Corpus striatum ^ 



Cerebral hemispl 



Cerebro-spinal ^ 



tract--" 

 Olfactory ner^e 



Olfactory 

 epithelium 



Vestibulo-spinal tract 

 Nucleus gracilis 



Retina of the eye 



X indicates the place where a tract crosses the median plane. 



FIG. 475. DIAGRAM REPRESENTING THE CONNEXIONS OP SOME IMPORTANT SENSORY AND MOTOR TRACT.- 



IN THE BRAIN. 



vary considerably at different levels of the spinal medulla. In Fig. 473 a 

 attempt has been made to present the present state of our knowledge of thee 

 great strands of white fibres. This diagram is not intended to represent any definit 

 level of the spinal medulla, though certain features are shown which occur onl 

 in the cervical region ; and in respect of other features, the arrangement foun 

 in lower regions of the spinal medulla has been introduced to render the diagrai 

 more serviceable. 



Much of the apparent complexity of this chart will disappear if the readf 

 recalls some general statements (p. 512) made with regard to the outstandin 

 features of the brain. It was then explained that when sensory nerves, comic 

 from the skin and muscles, enter the spinal medulla, they not only establis 

 relations with the motor nuclei and other spinal structures in the neighbourhoc 

 of their insertion, but also give rise, directly or indirectly (see Fig. 475) to man 



