452 THE BRAIN 



of grey matter, but each has also a superficial coating of 

 white fibres. The superior colliculi are larger and broader 

 than the inferior, but they are not so well defined nor yet so 

 prominent. 



A longitudinal and a transverse groove separate the quadri- 

 geminal bodies from one another. The longitudinal groove 

 occupies the median plane, and extends upwards as far as the 

 posterior commissure. From its lower end a short but well- 

 defined narrow band of white fibres, called the frenulum veli, 

 passes to the anterior medullary velum, a lamina which lies 

 immediately below the inferior pair of quadrigeminal promi- 

 nences, in the roof of the fourth ventricle. The upper part 

 of the longitudinal groove is occupied by the pineal body. 

 The transverse groove curves round below each of the two 

 superior colliculi and separates them from the inferior pair. 



Brachia of the Corpora Quadrigemina. The corpora 

 quadrigemina form the dorsal part of the mid-brain, but each 

 body is connected also with the corresponding lateral aspect 

 of the mesencephalon by a prominent white strand, which 

 is prolonged upwards and forwards under the projecting 

 pulvinar. The strands are called the brachia of the corpora 

 quadrigemina, and they are separated from each other by a 

 continuation, on the side of the mesencephalon, of the trans- 

 verse groove which separates the superior colliculi from the 

 inferior. 



Corpus Geniculatum Mediale. Closely connected with 

 the brachium of the inferior quadrigeminate body will be seen 



the medial geniculate body. It 



. 



CORP:GEN:LAT. is a little oval eminence, very 



sharply defined, which lies on the 

 side of the upper part of the 

 mesencephalon under shelter of 

 MEDIAL ROOT. the pulvinar of the thalamus. 



Connections of the Brachia 

 and the Termination of the Optic 

 Tract. There are two superior 



. . .... 



and two inferior brachia, right 



F1G ' ' R OIS ^d left, connected respectively 



with the corresponding superior 

 and inferior colliculi, and two optic tracts, right and left, which 

 pass backwards from the optic chiasma at the base of the brain. 

 Each inferior brachium runs upwards and forwards from the 



PULVINAR 



LATERAL ROOT. 



OPTIC TRACT 



