THE NERVOUS SYSTEM 1371 



valleculse as it crosses it. This ridge is notched at inten-als, and 

 is called the furrowed band. 



The nodule forms the anterior part of the inferior vermis, and is 

 composed of several laminae, which are largely concealed by the 

 uvula. It is connected on either side with the flocculus by a thin 

 semilunar band of white matter, which is the lateral portion of the 

 inferior medullary velum. 



The fissures of the inferior vermis are three in number, as follows : 

 postpyramidal, between the pyramid and the tuber valvulae ; pre- 

 Pytamidal, between the pyramid and the uvula ; and postnodular, 

 between the nodule and the uvula. 



The under surface of each hemisphere is mapped out into four 

 lobules, which are called, from behind forwards, the postero- 

 inferior lobule, the biventral lobule, the amygdala, and the 

 flocculus. 



The postero-inferior lobule is situated at the back part of the 

 under surface of the hemisphere. It is divided into four cur\'ed 

 parts by three curved fissures. The anterior t^vo parts are known 

 as the lobuliis gracilis, and the posterior two as the inferior semi- 

 lunar lobule. The right and left postero-inferior lobules, together 

 with the tuber valvulse, form the lobus tuberis. 



The biventral lobule is composed of curved laminae, and is some- 

 what triangular. The pointed end is directed backwards and 

 inwards, and it is connected with the pyramid by a faint ridge, 

 which, as stated, lies low in the sulcus valleculae. The base is 

 directed forwards towards the flocculus. The lobulus gracihs lies 

 external to it, and the amygdala is on its inner side. The biventral 

 lobule is divided by a sulcus into two portions, outer and inner ; 

 hence the name ' biventral.' The right and left biventral lobules, 

 together with the pyramid, form the lobus pyramidis. 



The amygdala (tonsil) forms a conspicuous prominence between 

 the uvula and the biventral lobule. It is situated in a depression 

 of the vallecula, which is known as the nidus avis (' bird's nest '), and 

 its direction is almost sagittal. It is connected with the narrow 

 part of the uvula by the furrowed band, which, as stated, lies low in 

 the sulcus valleculae. The right and left amygdalae, together with 

 the uvula, form the lobus uvulae. 



The flocculus (subpeduncular lobule) is a small irregular lobule 

 which is situated between the front of the biventral lobule and 

 the middle peduncle of the cerebellum. Internally it is connected 

 with the nodule by the lateral portion of the inferior medullary 

 velum. The right and left flocculi, together with the nodule, form 

 the lobus noduli. 



The fissures of the under surface of each hemisphere are as 

 follows : (i) a continuation of the postnodular sulcus, between the 

 biventral lobule and the flocculus ; (2) a continuation of the pre- 

 pyramidal sulcus, between the amygdala and the biventral lobule ; 

 (3) the pregracile, or anterior arcuate, sulcus, between the biventral 

 lobule and the lobulus gracilis ; (4) the mid-gracile, or middle arcuate 



