MEDULLARY VELA 535 



The superior peduncles are the brachia conjunctiva of 

 the cerebellum. They are composed of fibres which come, for 

 the most part, from the nucleus dentatus of the cerebellar 

 hemisphere. As they issue from the cerebellum, the 

 peduncle lies close to the medial sides of the corresponding 

 middle peduncles. They then proceed upwards towards the 

 inferior pair of quadrigeminal bodies. At first they form the 

 lateral boundaries of the upper part of the fourth ventricle, 

 but they converge, as they ascend on the dorsal aspect of the 

 pons, so that ultimately they overhang the fourth ventricle 

 and enter into the formation of its roof. They disappear 

 under cover of the quadrigeminal bodies, and their course 

 in the mesencephalon has been described already (p. 511). 



Medullary Vela. The medullary vela are closely associated 

 with the peduncles. They consist of two thin laminae of 

 white matter which are projected out from the white central 

 core of the cerebellum. The anterior medullary velum stretches 

 across the interval between the two brachia conjunctiva 

 (superior peduncles), with the medial margins of which it is 

 directly continuous. It is triangular in form, and is con- 

 tinuous below with the white matter of the cerebellum. 

 Spread out on its dorsal surface is the tongue-shaped prolonga- 

 tion of grey matter from the cortex of the cerebellum which 

 is termed the lingula, and issuing from its substance, close 

 to the inferior quadrigeminal bodies, are the two trochlear 

 nerves. 



The posterior medullary velum is somewhat more complicated 

 in its connections. It presents the same relation to the 

 nodule that the anterior velum presents to the lingula. It is 

 a wide thin lamina of white matter so thin that it is 

 translucent which is prolonged out from the white centre 

 of the cerebellum above the nodule. From the nodule it 

 stretches laterally to the flocculus, thereby bringing these 

 two small portions of the cerebellum into association with 

 each other. Where it issues from the white matter of the 

 cerebellum it might almost be said to be in contact with the 

 anterior medullary velum, but as the two laminae are traced 

 anteriorly they diverge from each other : the anterior velum is 

 carried upwards between the brachia conjunctiva of the cere- 

 bellum, whilst the posterior medullary velum turns downwards, 

 round the nodule, and ends in a slightly thickened free 

 crescentic edge. The cavity of the fourth ventricle is carried 



