THE SPINAL CORD AS A CONDUCTING PATH 619 



thalamus of the same side but in part also in the corpora quadrigemina of both 

 sides. 



(e) A few scattered bundles of ascending fibers are also found in the anterior 

 funiculus. They intermingle here with the descending tracts mentioned previously. 

 The fasciculi proprii or ground bundles are not mentioned separately in this enu- 

 meration, because parts of them have already been described under the heading 

 of the septomarginal and comma tracts. 



The Function of the Roots of the Spinal Cord. The Bell-Magendie 

 Law.^ — The general conclusion to be derived from the preceding 

 discussion is that the white matter of the spinal cord of the higher 

 animals is arranged in definite tracts which connect: 



(a) Different segments of this structure with one another, thus 

 forming the propriospinal paths, ^.e., a short or reflex system of 

 conduction. 



(6) The cord with the hindbrain, midbrain and forebrain, forming 

 a long or projection system of conduction. With the hindbrain the 

 connections are made over the posterior cerebellar tracts, the tracts 

 of GoU and Burdach, the spino-olivary and vestibulospinal bundles. 

 The midbrain receives its impulses by way of the spinotectal tracts 

 and discharges them over the rubrospinal. The forebrain (thalamus) 

 is entered through the spinothalamic tracts. From here the impulses 

 are relegated to the cerebrum, which organ, as has been stated above, 

 is not in direct afferent communication with the cord, because the 

 impulses directed to it from the latter structure, are first relayed 

 into lower nuclei and centers before they are finally distributed to the. 

 cerebral cortex. On the efferent side, however, the cerebrum is in 

 possession of a direct path in the shape of the anterior and lateral 

 pyramidal tracts. As has been emphasized repeatedly, the mere 

 entrance of an impulse into the cerebrum does not admit it to conscious- 

 ness; in fact, many of the reactions resulting in consequence of cerebral 

 activity "retain their reflex character as strictly as those evoked 

 exclusively with the help of the spinal cord. It is true, however, 

 that many of them are controlled by consciousness. They are then 

 converted into volitional acts, the p'receding afferent impulses haying 

 been received in consciousness as sensations of different qualities. 



We are now in a position to go one step farther and to inquire 

 how the different spinal tracts and especially those belonging to the 

 projection system, are connected with the distant receptors and ef- 

 fectors. It will be remembered that each spinal nerve arises by two 

 roots, an anterior or ventral, and a posterior or dorsal, and that these 

 roots finally unite to form a nerve. Centrally to their point of union, 

 the posterior group of fibers is associated with a colony of cells, which 

 form the so-called intervertebral ganglion. In 1811 Ch. BelP found 

 that the mechanical stimulation of the anterior group of fibers gives 

 rise to movements, while the posterior behaves negatively in this 



' Longet, Anat. et physiol. de la syst. nerv., 1847. 

 "^Ab. idea of a new anatomy of the brain, London, 1811. 



