SUMMARY OF SPINAL CORD 789 



The three systems : (1) Association and commissural. — ^Axones of spinal ganglion (afferent) 

 neurones bifurcate within the cord into cephalic and caudal branches which extend varying 

 distances upward and downward and terminate, (a) about cell-bodies whose axones are short 

 and terminate within the grey substance of the same side and in the same level as their cell- 

 bodies {Golgi neurones of type II); (b) about ceU-bodies whose axones pass without the grey sub- 

 stance, bifurcate into cephalic and caudal branches to terminate in the grey substance of the 

 same side but in various levels above and below (association fibres in the dorsal, lateral and ven- 

 tral fasciculi proprii); (c) about cell-bodies whose axones cross the mid-line to terminate either 

 in the same level of the grey substance of the opposite side, or bifurcate and the cephalic and 

 caudal branches pass in the fasciculi proprii to terminate in various levels of the grey substance 

 of the opposite side. The longer cephalic branches of (6) and (c) may terminate in the medulla 

 oblongata. All, associated with ventral root (efferent) neurones, belong to the neurone chains 

 for the so-called reflex activities. 



(2) The cerebral system. — (a) The cephalic branches of certain spinal ganglion neurones 

 ascend beyond the bounds of the spinal cord to terminate within the medulla. Those ascend- 

 ing from the spinal ganglia of lower thoracic and lumbo-sacral segments accumulate mesially 

 to form the fasciculus gracilis which terminates in the nucleus of this fasciculus; those arising 

 from the upper thoracic and cervical segments accumulate more laterally in the posterior funi- 

 culus to form the fasciculus cuneatus which terminates in the nucleus of the fasciculus cuneatus. 

 (h) The impulses transferred to the neurones of these nuclei are borne across the mid-line and 

 finally reach the sensory-motor area of the cerebral cortex, and cell-bodies here give rise to axones 

 which descend, some decussating in the medulla to form the lateral cerebrospinal fasciculus, 

 others form the uncrossed ventral cerebrospinal fasciculus which crosses the mid-line as it de- 

 scends the cord. Both of these fasciculi transfer their impulses either directly to efferent ven- 

 tral horn neurones, or to association neurones and these to the efferent neurones, (c) The 

 cephalic and caudal branches of spinal ganglion neurones terminate about cell-bodies in the grey 

 substance of the cord whose axones cross the mid-line and ascend laterally to terminate either 

 in the quadrigeminate bodies {spino-mesencephalic tract), or in the thalamus (spino-thalamic 

 tract), {d) Cell-bodies in thalamus and superior quadrigeminate bodies (receiving optic im- 

 pulses) and in the inferior quadrigeminate bodies (probably mediating auditory impulses), 

 give axones which cross the mid-line in the mesencephalon and descend, forming the thalamo- 

 spinal and mesencephalospinal tracts, to terminate in contact with the efferent neurones of the 

 cord. Axones from both sources descend in the lateral funiculus, while from the superior 

 quadrigeminate body, a separate bundle descends in the ventral funiculus as the sulco-marginal 

 {ventral mesencephalospinal) fasciculus, (e) The rubrospinal tract arises from cell-bodies in 

 the red nucleus (in the mesencephalon), crosses the mid-line and descends in the lateral funiculus 

 to transfer (probably cerebellar) impulses to the efferent neurones of the spinal cord. 



(3) The cerebellar system. — (a) The cephalic and caudal branches of spinal ganglion 

 neurones give telodendria about the cell-bodies forming the dorsal nucleus of the cord (Clarke's 

 column) and about cell-bodies situated in grey substances ventral to the dorsal nucleus ("Still- 

 ing's nucleus") and in the lateral horn. Axones arising from the cells of the dorsal nucleus 

 pass laterally to form the dorsal spino-cerebellar fasciculus which ascends into the cerebellum by 

 way of its inferior peduncle of the same side and terminates about cell-bodies of its cortex. 

 Axones arising from Stilling's nucleus and the lateral horn cells, of both the same and opposite 

 sides of the cord, accumulate to form the superficial ventro-lateral spino-cerebellar fasciculus, 

 which ascends to enter the cerebellum by way of its superior peduncle and terminate about the 

 cells of the cerebellar cortex, (b) A few axones arising in the roof nucleus of the cerebellum 

 probably descend in the anterior marginal fasciculus in company with the ventral vestibulospinal 

 tract to terminate upon the efferent neurones of the cord, (c) The inferior olivary nucleus, in the 

 medulla, is a cerebellar relay and its cell-bodies are associated with the neurones of the upper por- 

 tion of the same side of the spinal cord. Whether the axones arise in the olivary nucleus or 

 in the grey substance of the cord is uncertain, but the more usual supposition favours the cord 

 and thus the name, spino-olivary fasciculus is given them, (d) Among its other functions, 

 the cerebellum is concerned with equilibration. The vestibular nerve is the afferent nerve of 

 equilibration and a large mass of the axones arising from its nuclei of termination terminate 

 in the cerebellum, in the roof nuclei especially. Axones arising from cell-bodies in Deiters' 

 nucleus (its lateral nucleus of termination) and in the nucleus of its descending root descend 

 the cord in the lateral funiculus to form the (lateral) vestibulospinal tract, and also in the anterior 

 marginal fasciculus to form ventral vestibulospinal tract. Impulses borne by these axones reach 

 the efferent or motor root neurones. The rubro-spinal fasciculus, mentioned above also may 

 be possibly considered as belonging to the cerebellar system. 



Sympathetic relations. — The cell-bodies of the efferent neurones in the ventral horns are 

 of two general varieties: (a) those whose axones terminate upon skeletal muscle (somatic 

 efferent), and (6) those whose axones terminate in contact with cell-bodies of sympathetic 

 neurones, the splanchnic or visceral efferent neurones. The axones of the sympathetic neurones, 

 in their turn, terminate upon cardiac and smooth muscle (motor) and in glands (secretory). 

 Like the somatic, the visceral efferent neurones receive impulses within the ventral horns 

 'a) from the cephalic and caudal branches of spinal ganglion neurones, (b) the descending cere- 

 bro-spinal fasciculi, and (c) from either, by way of the fascicuh proprii and Golgi neurones of 

 type II. Their cell-bodies are situated for the most part in the dorsal portion of the lateral 

 horn (dorso-lateral group of cells), which is the only portion of the lateral horn present in the 

 thoracic region of the cord. Many of the visceral efferent fibres leave the spinal nerves distal 

 to the spinal ganglia and make the white communicating rami, thus going to the nearest sym- 

 pathetic ganglia; others pass on in the spinal nerve and its branches to terminate in more distal 

 sympathetic ganglia. Dogiel has described axones which arise in sympathetic ganglia and termi- 

 nate upon the cell-bodies of the spinal ganglia. Such convey sensory impulses which, however, 

 enter the spinal cord by way of the dorsal root branch of the spinal ganglion neurone. Such 

 afferent sympathetic neurones are relatively rare, the peripheral distribution of the ordinary 



