Till: ISTIIMrs. 679 



obliquely crosses, loses itself in the cerebellum by its supero-posterior 

 mity, arriving behind the testes, and passing beneath these small organs 

 by its jinti TO -int't Tior extremity, along with the band of Roil or supero-latcral 

 fasciculus of the cerebral peduncles. 



In studying the structure of the cerebellum, wo will see how these 

 peduncles comport themselves in its interior. 



5. Valve of Vieussen. (Fig. 323, 6.) 



This designation is given to a very thin, white lamella which unites, on 

 each side, the two anterior cerebellar peduncles. In shape it is nearly a 

 parallelogram. Its superior face is covered by the cerebellum ; the inferior 

 ei incurs in forming the floor of the cerebellar (fourth) ventricle. The two 

 / borders are joined to the peduncles this vulve unites ; the anterior is 

 attached behind the testes; while the posterior adheres to the anterior 

 vermiform eminence (liiujiictta laminosa) of the cerebellum. 



( uill has considered this lamella as a commissure of the anterior cere- 

 b-llar peduncles, and we think rightly; for we see it formed almost 

 exclusively of transverse fibres which run from one of these peduncles to 

 the other. These fibres are most apparent in front, where the membrane is 

 much thicker ; behind, they are mixed with some longitudinal fasciculi. 



6. Corpora Quadri'jemina or Bigemina. (Fig. 323, 7, 8.) 



These are four round eminences, placed in pairs, which surmount the 

 cerebral peduncles behind. The two posterior, the smallest, are also named 

 the titbi-rcnJn tt'sles, and the anterior pair the tubercula nates. 



The posterior corpora quadrigemina, or tubercula testes, are related, in front, 

 with the. anterior eminences : behind, with the anterior cerebellar peduncles 

 and the valve of Vieussens, from which they are separated by a transverse 

 groove, from the bottom of which arise the pathetici nerves. An oblique 

 baud unites them, outwardly, to that portion of the optic layer designated 

 the corpus geniculatuiit infi-nium. 



The anterior corpora quadrigemina, or tubercula nates, are distinguished 

 from the preceding not only by their larger volume, but by their colour, 

 which is grey, that of the testes being white. They are also rounder, nearer 

 e; id i other, and covered by the cerebral hemispheres; while the posterior 

 rather lie beneath the cerebellum. A curved groove isolates them, in front, 

 from the thalami optici. 



7. Thalami Optici. (Fig. 323, 9.) 



This name is given to that part of the upper face of the isthmus which 

 is situated in front of the corpora quadrigemina. These thalami are 

 tin T( fore placed above the anterior part of the cerebral peduncles. 



Lumr altogether than the corpora quadrigemina, and more so before 

 than behind, each exhibits a grey, slightly convex, and very irregularly 

 quadrilateral surface, covered by the velum interposition, which separates it 

 from the cornu Ammonis (pet hippocampi), and from the posterior pillars of 

 the cerebral trigonal (fornix). 



/ r, ,f, Ih/, they incline towards each other informing on the median 



line a some\vhat deep fissure, in which runs, from before to behind, two 



white longitudinal bands that will bo noticed hereafter as the anterior 



nclcf of the pineal gland. This fissure enters, behind, into the common 



