Byes ZOOLOGY. 
segmented. In all Vertebrates above the lamprey, the verte- 
bral column grows around the notochord, which finally 
Fie. 371, 
Fig. 369.—Transverse section through the spinal cord of a calf. a, anterior, 5, 
posterior longitudinal fissure ; ¢, central canal; d, anterior, ¢, posterior cornua; Jf, 
substantia gelatinosa; g, anterior column of the white substauce ; A, lateral, é, pos- 
terior column ; &, transverse commissures. —After Gegenbaur. 
Fig. 870.—Section through the vertebral column of Ammoceetes (lamprey). Ch, no- 
tochord; ¢s, chordal sheath ; m, spinal chord ; a, aorta; v, veins. 
Fig, 371.—Section through the spinal column of a young salmon. Ch, notochord ; 
cs, chordal sheath; m, spinal chord; , superior, 4’, inferior arch (rudimentary) ; a, 
aorta; v, veins.—After Gegenbaur. 
forms the central portion of the bodies of the vertebra, and 
in the higher Vertebrates is wholly effaced; the centra or 
