ORDER OF MEDULLATION 



791 



spinal ganglion neurone in the domain of the sympathetic supplying the needs for sensory 

 axones. 



In transverse sections of the spinal cord, the relative area of white substance 

 as compared with that of grey increases as the cord is ascended. The absolute 

 area of each varies with the locality, both being greatest in the enlargements. The 

 grey substance predominates in the conus medullaris and lower lumbar segments. 

 The white substance begins to predominate in the upper lumbar segments, not 

 because of the increased presence of ascending and descending cerebral and cere- 

 bellar axones, but because of the increased volume of the fasciculi proprii coinci- 

 dent with the greater mass of grey substance to be intersegmentally associated in 

 this region. In the thoracic region the greatly predominating white substance 



Fig. 622. — Graphic Representation of the Varying Amounts op Grey and White Sub- 

 stance AND OF THE VARIATIONS IN ArEA OF ENTIRE SECTIONS OF THE DIFFERENT SEGMENTS 



OF THE Spinal Cord. (From Donaldson and Davis.) 



(Based upon measurements from several adult human spinal cords.) 



Curves ^howinO area of cross seel ion of human spinol cord. 



■Whi^e mailer. 



•Grey maHer. 



-Enlire secHon. 



in m ly Y vi Mini i u ui n: 

 CERVICAL 



Y \i YH VUI 

 THORACIC 



X XI XII I H m IN'YI llllllTVi 

 LUMBAR SACRAL 



is composed mostty of the axones of long course. The greatly increased absolute 

 amount of white substance in the cervical region is due both to the greater ac- 

 cumulation of cerebral and cerebellar axones in this region and to the increased 

 volume of the fasciculi proprii of the cervical enlargement. 



ORDER OF MEDULLATION OF THE FASCICULI OF THE CORD 



The axones of the spinal cord begin to acquire their myeUn sheaths during the fifth month of 

 intra-uterine hie and myeUnization is not fully completed till between the fifteenth and twentieth 

 years. In general, axones which have the same origin and the same locality of termination — 

 the same function — acquire their sheaths at the same time. While it has been proved that the 

 medullary sheath does not necessarily precede the functioning of an axone, it may be said that 

 those fascicuh which first attain complete and definite functional abiUty are the first to become 

 meduUated. At birth all the fasciculi of the spinal cord are meduUated except Helweg's fasci- 

 culus, and occasionally the lateral and ventral cerebro-spinal tracts. The latter tracts vary 

 considerably and in general may be said to become meduUated between the ninth month (before 

 birth) and the second year. As indicated by their medullation, those axones by which the cord 

 is enabled to function as an organ per se, that is, the axones making possible the simpler reflex 

 activities, complete their development before those axones which involve the brain with the 

 activities of the cord. 



According to Flechsig and van Gehuchten, and investigators succeeding them, the following 

 is the order in which the axones of the cord become meduUated: — 



(1) The afferent and efferent nerve-roots and commissural fibres of the grey substance. 



(2) The fascicuh proprii, first the ventral, then the lateral, and last the dorsal, fasciculus 

 proprius. 



(3) The fasciculus cuneatus (Burdach's column) and Lissauer's zone — the area of those 

 ascending spino-cerebral fibres which run the shorter course and which convey impulses from 

 the upper limbs, thorax and neck. 



(4) Fasciculus gracUis (GoU's column). 



(5) The dorsal spino-cerebeUar fasciculus (direct cerebeUar tract). 



(6) The superficial antero-lateral spino-cerebeUar fasciculus (Gowers' tract). 



_ I (7) The lateral cerebro-spinal fasciculus (crossed pjTamidal) and the ventral cerebro- 

 spinal fasciculus (direct pyramidal tract). 



(8) The spino-olivary or Helweg's (Bechterew's) fasciculus. 



