890 THE PONS AND CEREBELLUM. 



path is also believed to exist. The mesial longitudinal bundle is in part a 

 descending path from visual and auditory centres to spinal, especially cervical, 

 motor mechanisms (Cajal, van Gehuchten). 



Of the paths ascending through the bulb from the spinal cord, the chief 

 are (1) The continuation from the dorsal columns of root fibres, that by a second 

 link pass from the dorsal column nuclei to the fillet of the crossed side ; 



(2) the two spino-cerebellar ; one (the restiformal) chiefly uncrossed from the 

 cord and entering the inferior peduncle of the cerebellum, the other 

 (the conjunctival) entering with the superior peduncle of the cerebellum. 

 With this latter pass probably spino-bulbar, spino-mesencephalic, and spino- 

 thalamic paths toward end-stations in and in front of the bulb itself. 



(3) The mesial longitudinal bundle contains fibres ascending (Held, Tschermak) 

 from v. Lenhossek's commissural cell-group of the ventral horn of the cervical 

 cord to reach motor cerebral nuclei, especially of the eye-muscles. The path 

 from the dorsal column nuclei by the crossed fillet extends to the diencephalon 

 (optic thalamus) and in part to the cerebral cortex, especially its parietal region. 

 Of the function of the inferior olive little is known : its connection with 

 paths from the vestibular nerve is suggestive. 



THE METENCEPHALON OR EEGION OF THE PONS VAROLII AND 



CEREBELLUM. 



If in the frog all the brain anterior to the metencephalon be 

 removed, the animal can still walk, spring, and swim. The croak reflex 

 is elicitable, but not readily ; it is annulled when the metencephalon is 

 destroyed. The animal reacts on the turn-table perfectly, but this 

 reaction is destroyed when the ablation is extended to the root of the 

 trigeminus. Goltz's reaction to the tilted board is perfect as regards 

 head movement, imperfect as regards correction of the posture of the 

 body by crawling up the board. The animal, if undisturbed, remains 

 inert ; if the ablation include the cerebellum and fore-part of the 

 metencephalic floor, the creature becomes active, crawling about until it 

 reaches some corner that blocks further progress. The condition 

 resembles that of the annelid Nereis after removal of the supra- 

 cesophageal ganglion. 1 It jumps very rarely. That its locomotor co- 

 ordination is good, is shown by its climbing over obstacles successfully ; 

 in swimming it rarely uses the bilateral stroke, but swims " like a dog." 2 

 In the condition of which continual crawling is characteristic, there is 

 extraordinary activity of the swallowing reflex. Anything touching 

 the muzzle is snapped at, taken into the mouth, and swallowed. The 

 " embrace " reflex is in the male similarly active, more so than in the 

 normal animal, even at the height of the breeding season. The re- 

 spiratory movements appear normal. Even when the front part of 

 the metencephalon has been removed, the frog at once rights itself when 

 placed on its back. 



In the rabbit similar ablation apparently destroys the power of 

 progression. A condition likened to strychnisation 3 sets in, and the 

 skin of the head and trunk seem " hypersesthetic." When the muzzle 

 is touched the homonymous fore-limb is lifted toward it, and when that 

 is restrained the contralateral fore-limb is brought up as though as an 

 alternative manoeuvre. 



1 S. S. Maxwell, Arch. f. d. ges. PhysioL, Bonn, 1897, Bd. Ixvii. S. 263 (Loeb's Lalora- 

 tory Archives, Bd. ii.). 



2 Schrader, Arch. f. d. ges. PhysioL, Bonn, 1887, Bd. xli. 



3 Christiaiii, Verhandl. d.physiol. Gesellsch. zu Berlin, in Arch. f. PhysioL, Leipzig, 1884. 



