THE SPINAL CORD AS A CONDUCTING PATH 613 



the gray matter of the opposite side by way of the anterior white commissure. 

 We shall see later on that these fibers arise in the motor cortex of the cerebrum 

 (cells of Betz) of the same and opposite side, and are therefore descending in their 

 character. 



(6) Fasciculus anterior proprius, also called the anterior ground bundle or 

 root zone. This column occupies the area next to the anterior root and extends 

 throughout the cord. The fibers composing it are commissural in their character, 

 i.e., they bring different segments of the gray matter into functional relation. 

 This end they accomplish by passing to higher as well as to lower levels of the cord, 

 where they reenter the gray matter and make connections with other cells. 



2. The lateral funiculus embraces the white matter between the anterior and 

 posterior roots and is composed of the : 



(a) Fasciculus cerebrospinalis lateralis, also called the lateral or crossed pyram- 

 idal tract. It occupies the posterior area of this funiculus, but its position varies 

 somewhat at different levels of the cord. In the lumbar region, it comes right to 

 the surface, while in the cervical and thoracic regions it remains at some distance 

 from it. It is covered here by a layer of fibers composing the fasciculus cere- 

 bellospinalis. Its fibers arise in the motor area of the cerebrum (cells of Betz), 

 but cross to the opposite side of the body in the medulla. In their downward 

 course through the cord they terminate successively at different levels of the gray 

 matter so that the size of the entire column diminishes gradually from above 

 downward. 



(b) Fasciculus spinocerebellaris, also designated as the direct cerebellar or 

 Flechsig's column. It lies externally to the crossed pyramidal tract. Its fibers 

 take their origin in the cells of Clark's column. From here they pass obliquely 

 outward and upward and finally terminate in the cerebellum, where they decussate 

 in part in the superior vermiform lobe of this structure. 



(c) Fasciculus anterolateralis superficialis, also known as Gower's tract. It 

 occupies the external realm of the lateral funiculus in front of the crossed pyra- 

 midal tract and extends forward as far as the anterior roots. It begins in the 

 lumbar segment and forms a compact strand through the entire cord. I'he largest 

 number of its fibers arise in the opposite gray matter and cross the midline by way 

 of the white commissure. The uncrossed fibers find their origin in relation with 

 axons which have passed through the gray commissure and have come from cell- 

 bodies in the gray matter of the opposite side. In the brain-stem this column 

 divides into several groups of fibers which terminate in the reticular nuclei, the 

 cortex of the cerebellum, the tectum, the substantia nigra and the thalamus. 



(d) Fasciculus lateralis proprius or lateral ground bundle. This tract forms a 

 narrow layer next to the external surface of the gray matter. It is believed to be 

 composed of efferent and afferent fibers, the former being situated in front. Its 

 function seems to be associative, because its fibers originate in cells of the spinal 

 gray matter and terminate at levels above and below their points of origin. 



3. The posterior funiculus comprises the white matter between the posterior 

 median fissure and the posterior roots. It consists of the : 



(a) Fasciculus gracilis, also called the column of GoU or the posteromedian 

 tract. It is situated next to the posterior fissure and begins with the posterior 

 root of the coccygeal nerve. Beginning at this level, it gradually increases in size 

 owing to the acquisition of the root fibers of higher nerves of the same side. Above 

 the fifth thoracic nerve it retains its caliber or becomes even somewhat smaller, 

 because whUe it ceases here to receive root fibers, it continues to give off collaterals 

 to the successive segments of the gray matter. It terminates in the nucleus funi- 

 culi gracilis of the medulla. 



(b) Fasciculus cuneatus, also known as the column of Burdach or posterolateral 

 tract. It lies next to the posterior horn and begins in the middle thoracic region. 

 As it acquires new fibers constantly, its size increases from below upward until it 

 terminates in the nucleus funiculi cuneati of the. medulla. Its fibers are derived 

 from the successive posterior roots of the spinal nerves of the same side as well as 



