LOBES OF THE CEREBELLUM. 213 



(b) ; but this, and the furrowed band will be seen in a subsequent dissec- 

 tion (p. 214). Behind the uvula is a tongue-shaped body, named pyramid 

 (fig. CO, </), which is elongated from side to side, and is^marked by trans- 

 verse laminae. Further back are certain transverse pieces (<?), extending 

 between the posterior lobes of the hemispheres, of which they were con- 

 sidered by Reil to be the commissures. 



Laminae. The surface of the cerebellum is covered by plates or laminae 

 (fig. 68), instead of convolutions, which form segments of circles with 

 their convexity directed backwards. On the upper aspect the anterior 

 laminae pass from the one hemisphere to the other, with only a slight 

 bending forwards in the superior vermiform process ; but those on the 

 under aspect join the sides of the different commissures in the median 

 fissure. 



Sulci. Between the laminae are sulci, which are lined by the pia mater, 

 and reach to different depths : the shallower separate the laminae ; but the 

 deeper limit the lobes, and reach downwards to the white substance of the 

 interior. Here and there the sulci are interrupted by cross laminae. 



Structure of the lamince. On cutting across the laminae of the upper 

 surface on the right side they will be seen to possess a white internal, and 

 a gray external layer (fig. 68). The white part is derived from a central 

 medullary mass ; and dividing, like the branching of a tree, it ends in 

 small lateral offsets which enter the subdivisions of the laminas. 



Besides the white stalk of the lamina}, derived from the central mass, 

 there are other white fibres which pass from one lamina to another beneath 

 the sulci. 



The stratum of gray matter enveloping the white substance resembles 

 the cortical covering of the . convolutions of the cerebrum. It is con- 

 structed of two strata, inner and outer, which can be distinguished by a 

 difference in their color. The superficial stratum is clear gray, and about 

 equal to the other in thickness ; but the deeper one is of a rust-color, and 

 is generally thickest in the hollows between the laminae. Between the 

 two a layer of ramified cells (Purkinje) may be recognized with the micro- 

 scope. 



LOBES OF THE HEMISPHERE. Each hemisphere is subdivided into lobes 

 on both aspects. 



On the upper surface there are two lobes, anterior and posterior, which 

 are separated by a sulcus, but the interval between them is not well marked. 

 The anterior or square lobe extends back to a level with the posterior edge 

 of the vermiform process ; and the posterior reaches thence to the great 

 horizontal fissure at the circumference. 



On the under surface of the cerebellum (fig. 66), there are five lobes ; 

 and three of them are separated by sulci amongst the lamina? of the hemi- 

 sphere, but they are scarcely more distinct than the lobes on the upper 

 surface. Beginning behind, the student will meet first the posterior lobe 

 (&), which joins the comrnissural laminae behind the pyramid in the val- 

 ley. Next in succession is the slender lobe (/), which is connected with 

 the posterior part of the pyramid, as well as with the other transverse 

 laminae behind that body. And lastly, attached to the side of the pyramid, 

 is the biventral lobe (h). 



The two other lobes, though smaller are more separate, and appear be- 

 tween the biventral lobe and the medulla oblongata : One of these is the 

 amygdaloid lobe (#), which projects into the vallecula opposite the uvula, 

 and touches the medulla oblongata. The other is a small pyramidal slip, 



