254 THE RHOMBENCEPHALON. 



Though larger it is the counterpart of the lingula on the superior 

 velum. It is bounded by the sulcus valleculae on either side. 

 The inferior medullary velum extends laterally from the nodule, 

 and in part blends with the brachium pontis of the cerebellum. 

 In front of the tonsil, a layer of gray matter (pedunculus flocculi) 

 appears on the velum. That gray matter enlarges more exter- 

 nally to a smah 1 tufted mass, called the flocculus, in which the velum 

 ends. Embryologically, the flocculus is the oldest lobule of the 

 human cerebellum, as is the floccular sulcus (postnodular sulcus) 

 which bounds it, the first one formed. The flocculus is very 

 small and rudimentary in man. It is divided into an anterior 

 and a posterior part, the latter being called the secondary floccu- 

 lus. The flocculus is separated from the tonsil and the biventral 

 lobule by the postnodular sulcus. The whole line of structures, 

 namely, the nodule, velum, peduncle and 'flocculus, form the 

 lobe of the nodule. 



Uvula and Tonsils, Lobus Uvulae (Figs. 79 and 80). The 

 uvula (uvula vermis) comprises a considerable part of the vermis 

 inferior behind the nodule. It broadens backward and is widest 

 next the pyramid. Bounded on either side by the sulcus vall- 

 eculae, it projects into the valley like the uvula into the isthmus 

 of the fauces. It comprises one large branch of the arbor vitae 

 which bifurcates near its origin into two laminae and presents 

 at the surface six or eight small gyri. A slight ridge, the fur- 

 rowed band, joins it to the tonsil (tonsilla cerebelli) in the hem- 

 isphere. From the furrowed band the tonsil expands downward 

 and backward, forming a lobule of nearly a dozen sagittal gyri. 

 The tonsil overhangs the side of the uvula and conceals the fur- 

 rowed band, medially; and, behind, it conceals the connecting 

 ridge between the pyramid and biventral lobule. Its large size 

 makes it a prominent feature of the human cerebellum. The 

 fossa containing the tonsil is the bird's nest (nidus avis). Be- 

 hind the uvular lobe, composed of the above three lobules, is the 

 prepyramidal sulcus. 



Pyramid and Biventral Lobules, Lobus Pyramidis (Figs. 

 79 and 80). As seen from the surface, three or four distinct 

 gyri make up the pyramid (pyramis vermis); in reality, it covers 



