CONDUCTION PATHS 895 



may hear, understand and speak them. This is called "word-blindness." This area is nearest 

 the special area of vision on the one hand and on the other hand, is continuous into the area to 

 which word-understanding is attributed. For purposes of writing, it mast be associated with 

 the motor area for the muscles of the hand in the precentral gyrus. 



While the motor area for speech is most functional in the left hemisphere, the remaining 

 areas concerned are probably equally developed in the two hemispheres. 



III. GENERAL SUMMARY OF SOME OF THE PRINCIPAL 

 CONDUCTION PATHS OF THE NERVOUS SYSTEM 



In the following summary the arable numerals indicate paragraphs in which are mentioned 

 the nuclei or gangUa containing the ceU-bodies of the neurones interposed in the chains; the 

 small letters indicate the different names given to the different levels of the pathways through 

 which their fibres run. For detailed descriptions of either nuclei or pathways see pages de- 

 scribing them. Only the more common neurone chains are followed here. 



I. The Spino-cerebral and Cerebro-spinal Path 



A. The ascending system of neurones, (fig. 705) 



1. Spinal ganglion — neurone of first order. 



(a) Terminal corpuscles and peripheral process of T-fibre. 



(b) Dorsal or afferent root of spinal nerve. 



(c) Ascending branch of bifurcation of dorsal root fibre in fasciculus gracilis, or 

 fasciculus cuneatus of spinal cord. 



2. Nucleus of fasciculus graciUs or nucleus of fasciculus cuneatus in medulla oblongata — 



neurone of second order. 

 (a) Internal arcuate fibres. ' 



(6) Decussation of lemniscus. 



(c) Interolivary stratum of lemniscus of opposite side. 



(d) Medial lemniscus. 



3. Hypothalamic nucleus and lateral nucleus of thalamus — neurone of third order. 



(a) Internal capsule, posterior segment of fronto-parietal portion. 



(6) Corona radiata, fronto-parietal part. 



(c) Posterior central gyrus of somsesthetic area of cerebral cortex. 



B. Descending system of neurones (fig. 706). 



1. Giant pjTamidal cells of precentral gyrus of somsesthetic area. 



(a) Corona radiata, fronto-parietal part. 



(6) Internal capsule, middle segments of fronto-parietal portion. 



(c) Basis of the cerebral peduncle and the peduncle. 



(d) Pyramid of medulla oblongata, 

 (gi) Decussation of pyramids. 



(/I) Lateral cerebro-spinal fasciculus (crossed pyramidal tract), 

 (e^) Ventral cerebro-spinal fasciculus (direct or uncrossed pyramidal tract). 

 (/2) Gradual decussation of latter in cervical and upper thoracic regions of spinal 

 cord. 



2. Cells of ventral horn of spinal cord of opposite side, 

 (a) Ventral or efferent roots of spinal nerves. 



(6) Peripheral nerve-trunks directly to skeletal muscles or indirectly to smooth 

 muscle or glands by way of sympathetic neurones. 



II. Short 'Reflex' Paths of Spinal Cord 



1. Spinal ganglia. 



(a) Terminal corpuscles and peripheral process of T-fibres. 



(5) Dorsal root of spinal nerve. 



(c) Collaterals and descending branches of bifurcation of dorsal root fibres in spinal cord 



(d) Directly to ventral horn cells of same level of spinal cord. 



(e) Or, more commonly, to same through intermediation of Golgi cell of type II. 



if) Or to neurones of fasciculi proprii to ventral horn cells of other levels of spinal cord. 



2. Ventral horn cells of same (chiefly) and opposite side and thence by way of ventral roots 



and peripheral nerve trunks directly to muscles. 



3. Dorso-lateral group of ventral horn cells of same (chiefly) and opposite sides and 



thence by ventral root fibres to cell-bodies in sympathetic gangUa. 



4. Sympathetic axones to smooth muscle or glands. 



III. Cerebral Path for the Cranial Nerves, Exclusive of Those of Special Sense 

 A. Ascending system of neurones. 



1. Gangha of origin of sensory components of vagus, glossopharyngeus, glosso-palatine 



and trigeminus, 

 (a) Peripheral arborisations and afferent peripheral branches of T-fibres of same. 

 (6) Central branches of T-fibres of same (sensory nerve roots). 



2. Nuclei of termination of central branches (bifurcated and unbifurcated) in medulla 



oblongata, 

 (a) Reticular formation, internal arcuate fibres and medial lemniscus of the opposite 

 side. 



