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system to their entrance into the chorda sheath. Sagittal sections, 
however, show that large cells lying in the central nervous system, 
latero-ventral to the neural canal give rise to fibres that unite into 
groups at intervals corresponding to the openings in the chorda sheath. 
On leaving these cells the fibres take a direction almost directly ven- 
tral, and, on nearing the surface of the spinal cord, turn laterally 
towards the openings in the chorda sheath (fig. 1). Moreover, when, 
as easily happens, the spinal cord is torn away from the chorda sheath 
above which it lies, these fibres are pulled out beyond the surround- 
ing nervous tissue towards the sheath, thus demonstrating their close 
connection with it (fig. 2). As far therefore as may be determined 
Fig. 1. Fig. 2. 
Fig. 1. Gold-chloride cross-section through spinal cord and notochord of Amphioxus. 
Ch. chorda. Ch.sh. chorda sheath. n.c. cells of central nervous system. n.ca. neural 
canal. m.fb. motor nerve fibres. m.pl. plate through which the motor fibres pass. 
v.fb. fibres to notochord (diagramatically represented). v.pl. plate through which the 
fibres to notochord pass. x. cells in the position of the cells in which the fibres to the 
notochord arise (not actually seen in cross-section as represented). 
Fig. 2. Section stained with bleu de Lyon. Sagittal, but not quite true. The 
section passes at a nearer the axial line than at 5, hence passes at a through the cells 
from which fibres go to the chorda, and at 6 through the openings in the chorda sheath. 
In sectioning, the spinal cord has been torn from the chorda sheath to which however 
the fibres (v. fd.) are still attached. Ch. chorda. Ch.sh. chorda sheath. 7. fb. longi- 
tudinal fibres in spinal cord. n.c. cells in central nervous system. op. openings in 
chorda sheath. pg. pigmented cells near the floor of neural canal. sp. space through 
which the spinal cord has been torn away from the chorda. ».fb. fibres passing to the 
chorda sheath. 
from sagittal sections, it is evident that the fibres which enter the 
chorda sheath are prolongations of cells lying in the central nervous 
system. 
It is well known that the motor nerve fibres of Amphioxus leave 
the central nervous system separately, and not in large bundles in 
