10 Anatomy of the Nervous System 



cerebral ganglia, though the latter are not very evident in 

 gross dissection. 



An almost imperceptible dorsal median sulcus (sulcus 

 medianus posterior) runs along the dorsal middle line and a 

 deep groove, the ventral median fissure (fissura mediana 

 anterior), occurs in the corresponding position ventrally. A 

 short distance to each side of the dorsal median sulcus is 

 another fairly distinct groove, in which the dorsal roots of 

 the spinal nerves enter the cord. This is the dorso-lateral 

 sulcus (sulcus lateralis posterior). The line of attachment 

 of the ventral roots is indicated by a much fainter depression, 

 the ventro-lateral sulcus (sulcus lateralis anterior). 



A dorsal view of the entire brain (Plate I.) shows the 

 three primary subdivisions, the cerebral hemispheres not 

 being sufficiently developed in the rat to conceal entirely 

 the more posterior sections. Anteriorly, the forebrain or 

 prosencephalon is represented by the cerebral hemispheres 

 and the olfactory bulbs; posteriorly, the hindbrain or rhomb- 

 encephalon is represented by the cerebellum and the medulla 

 oblongata; while between the cerebral hemispheres and the 

 cerebellum, appear the posterior colliculi of the midbrain or 

 mesencephalon. 



In the hindbrain, the cerebellum appears as a massive 

 thickening of the roof in the anterior part of the region, 

 which has attained so great a size as completely to conceal 

 the large cavity of the hindbrain, the fourth ventricle. Its 

 surface is thrown into numerous transverse folds, and shows 

 a division into different regions, of which the conspicuous 

 ones are the median vermis, the large paired cerebellar 

 hemispheres (lobuli ansiformes), at each side of it, and the 

 small, stalked floccular lobes projecting laterally. The 

 visible part of the floccular lobe is the paraflocculus, which 

 forms the greater part of this lobe in the rodent, the flocculus 

 being only an inconspicuous lobule at the base of the stalk. 



