688 THE NERVOUS SYSTEM. 



fissure. The anterior of the two subdivisions is named the slender lobe ; and the 

 posterior, the inferior semilunar or posterior inferior lobe. These fissures and lobes 

 are here arranged, from before backward, in a schematic form : 



UNDER SURFACE OF THE CEREBELLUM. 



Worm. Hemisphere. 



Nodule. Flocculus. 



Post-nodular fissure. 

 Uvula. Amygdala. 



Pre-pyramidal fissure. 

 Pyramid. Biventral lobe. 



Post-pyramidal fissure. 



( Slender lobe. 

 Tuber valvulae. < Post-gra 'die fissure. 



( Inferior semilunar lobe. 



The chief fissures of the under surface, as stated above, are three in number, 

 and are not so regularly disposed as on the upper surface. (1) The post-nodular 

 fissure in the worm courses transversely across it, separating the nodule in front 

 from the uvula behind. When it reaches the hemispheres it passes in front of the 

 amygdala, and then crosses between the flocculus in front and the biventral lobe 

 behind, and joins the anterior end of the great horizontal fissure. (2) The pre- 

 pi/ramidal fissure crosses the worm between the uvula in front and the pyramid 

 behind, then curves laterally behind the amygdala, and passes forward along the 

 outer border of this lobe, between it arid the biventral lobe, to join the post-nodular 

 sulcus. (3) The post-pyramidal fissure passes across the worm behind the pyramid 

 and in front of the tuber valvulae, and in the hemispheres courses behind the 

 amygdala and biventral lobes, and then along the outer border of the biventral 

 lobe to the post-nodular sulcus. It cuts off at least two-thirds of the inferior 

 surface of the hemisphere. From it a secondary sulcus springs, and coursing 

 forward and outward divides this surface into two parts and falls into the great 

 horizontal fissure. This sulcus is termed the post-gracile fissure. 



THE LOBES OF THE INFERIOR SURFACE OF THE CEREBELLUM. 



The Nodule and Flocculus. The nodule is a distinct prominence, forming the 

 anterior extremity of the inferior worm. It projects into the roof of the fourth 

 ventricle, and can only be distinctly seen after the cerebellum has been separated 

 from the medulla and pons. On each side of the nodule is a thin layer of white 

 substance, named the inferior medullary velum. It is semilunar in form, its 

 convex border being continuous with the white substance of the cerebellum ; it 

 extends on either side as far as the flocculus, which it connects with the nodule. 

 The flocculus is a prominent, irregular lobule, situated just in front of the biventral 

 lobe, between it and the middle peduncle of the cerebellum. It is subdivided into 

 a few small laminae, and is connected to the inferior medullary velum by its central 

 white core. 



The Uvula and Amygdalae. The uvula occupies a considerable portion of the 

 inferior worm ; it is separated on either side from the amygdala by a deep groove, 

 the sulcus valleculce, at the bottom of which it is connected to the amygdala by 

 a commissure of gray matter, indented on its surface, and called &e furrowed band. 

 It is marked on its surface by three or four transverse fissures. The amygdalae, 

 or tonsils, are rounded masses, situated in the lateral hemispheres. Each lies in 

 a deep fossa between the uvula and the biventral lobe ; this fossa is known by the 

 name of the bird's nest (nidis avis). 



