367 



runs ventro-niesially through the mesial thickening of the granular 

 layer, curves down behind the velar and trochlearis decussations and 

 enters the tectum mesial to the first and second bundles. After enter- 

 ing the tectum the fibers of the tract are spread in small bundles 

 through the whole width of the tectum and continue straight forward. 

 The bundles lie in the outer part of the central cellular zone and 

 beneath the fiber zone of the tectum. Occasionally small fasciculi or 

 single fibers separate from the bundles and bend upward into the 

 fiber zone. Since these fibers are much coarser than any others in 

 the tectum they could be easily followed in the fiber zone, but in fact 

 they are quickly lost, sometimes after being traced a short distance 

 toward the median line. They probably lose their sheaths upon enter- 

 ing the fiber zone and soon end. Only a few of the most mesial 



tctecto-csr. 

 S/Bindcatm 



'nucvLsc.ep 



Fig. 3. 



Fig. 4. 



The figures are all drawn with the camera, Fig. 5 at a higher magnification than 

 the others. 



Fig. 1 — 4. Transverse sections through the region of the cerebellum and velum 

 of Scyllium canicula. Fig. 1 is the most caudal section drawn ; one section intervenes 

 between it and Fig. 2, two sections between Figs. 2 and 3, and two sections between 

 Figs. 3 and 4. The cleft between the cerebellum and tectum in which the trochlearis 

 runs is drawn in black. 



a. a bundle of fine medullated fibers which run from the cerebellum through 

 the n. b. M. and decussate mesial to the f. I. d. c. cerebellum, c. c. cerebellar commis- 

 sure of fine fibers belonging to the molecular layer. The dotted line indicates the line 

 of separation of granular and molecular layers. The same commissure appears at the 

 top of the Figs. 1 — 4, where medullated fibers reach it. dec. v. decussatio veli. f.l.d. 

 fasciculus longitudinalis dorsalis. n. b. M. that portion of the central grey which is in 

 continuity with the corpus interpedunculare and forms the greater part of the end- 

 nucleus of Meynert's bundle, mtc. magn. nucleus magnocellularis tecti. nuc. vise. ep. 

 nucleus visceralis cerebelli. pi. ch. plexus chorioideus of the fourth ventricle, t. tec- 

 tum opticum. tr. tecto-cer. tractus tecto-cerebellaris. IV trochlearis nerve. IV dec. 

 decussation of the same. V trigeminus. Vs., Vm. sensory and motor roots of the tri- 

 geminus. V. r. m. radix mesencephalica trigemini. 



