XXXII] THE SPINAL BULB 255 



Dog. The lower olive is much less conspicuous in lower animals 

 than in man ; in most sections it appears as a double lamina placed 

 obliquely. The 12th n. fibres run laterally of the lower olive. The 

 bulbar root of the 5th forms a half-moon shaped bundle, more 

 distinct and more compact than in man. 



5. Section through the lower part of the 4th ventricle. 



The central canal has now opened into the 4th ventricle ; the 

 nucleus of the hypoglossal forms a conspicuous round mass near 

 the raphe and close under the floor of the ventricle, dorso- 

 laterally, is the dorsal nucleus, and then the sensory nucleus of 

 the 9th and 10th nerves. 



Ventro-laterally of the nucleus of the funiculus gracilis is the 

 nucleus of the funiculus cuneatus, distinct from the nucleus of 

 the funiculus gracilis by its larger cells ; the fibres of these are 

 now mixed up with the grey substance. 



Laterally of and on a level with the lower part of the dorsal 

 9th 10th nucleus is the solitary bundle. 



Note : 



On the dorsal surface of the nucleus of the funiculus gracilis, 

 the attachment of the thin membrane the ligula, forming the 

 roof of the ventricle (probably torn). 



Laterally of the nucleus of the funiculus cuneatus the rather 

 large mass of nerve fibres the restiform body (formed from 

 cerebellar tract, external and internal arcuate fibres). 



Laterally of the solitary bundle and stretching dorsally on the 

 medial side of the nucleus of the funiculus gracilis are a number 

 of small bundles o nerve fibres, the bundle formation (descend- 

 ing fibres of the vestibular nerve [8 v.]), (cp. 6). 



Dorsally and medially of the bundle formation, i.e. chiefly 

 between the nuc. f. gr. and the 9th and 10th n. nuclei, a small 

 amount of grey substance without nerve cells the lower end of 

 the median nucleus of the vestibular nerve. 



The internal arcuate fibres are very numerous. 



The internal arcuate fibres starting dorsally and just laterally of 

 the solitary bundle chiefly cross in the dorsal part of the raphe ; 

 those starting more laterally, apparently from the n. fun. cun., run 



