1374 



A MANUAL OF ANATOMY 



geminal bodies. Immediately below the inferior pair of quadri- 

 geminal bodies the fourth pair of cranial nerves emerge from the 

 superior medullary velum, on either side of the frenulum veli. The 

 tract of Gowers, after having traversed the formatio reticularis 

 of the medulla oblongata and the dorsal part of the pons Varolii, 

 passes into the superior medullary velum, and then desends in the 

 superior cerebellar peduncle to the cerebellum. 



The inferior or posterior medullary velum is a thin lamina of white 

 matter, which consists of three parts — median and two lateral, right 

 and left. 



The median part supports dorsally the nodule of the inferior 

 vermis. It is a prolongation of the white matter of the corpus 

 trapezoides of the vermis, and lies on the upper or ventral aspect of 

 the nodule, to which it is adherent. As it leaves the white matter 



Layer of Purkinje's Cells 



...Pia Mater 



Molecular Layer 



Granular Layer 

 ... White Medullary Substance 



Fig. 576. — Structure of a Lamina of the Cerebellum (highly 



magnified). 



it is contiguous to the superior medullary velum, but the two 

 laminae take different directions. The superior medullary velum 

 passes upwards between the dorsal parts of the superior peduncles of 

 the cerebellum. The median part of the inferior medullary velum 

 passes ventralwards and then downwards. It is succeeded in a 

 downward direction by the ependymal epithelium and pia mater 

 (tela choroidea inferior), which form a large portion of the lower 

 part of the roof of the fourth ventricle. The middle part of the 

 inferior medullary velum forms the upper portion of the lower part 

 of the roof of the fourth ventricle. 



Each lateral part of the inferior medullary velum extends out- 

 wards to the corresponding flocculus in the form of a semilunar 

 band. The ventral surface of this band is directed towards the 

 fourth ventricle, and the dorsal surface is related to the amygdala or 

 tonsil. One border of the band is free and concave, whilst the other 

 is continuous with the white matter of the corresponding cerebellar 

 hemisphere. 



