106 



MESENCEPHALON. 



The superficial fibres are continuous laterally and above with the fibres of the 

 brachium of ths inferior quadrigeminal body, and laterally and below with those of 

 the lower fillet. On the other hand, if the fibres of the lower fillet are traced down- 

 wards, they are partly found as we have already seen (p. 104) to be continuous with 

 fibres of the trapezium ; which again is connected with the principal nucleus of the 

 auditory nerve (cochlear division) of the opposite side (Flechsig). This would 

 appear to indicate a close connection between these posterior or inferior quadrigemi- 

 nal bodies and the auditory nerve, and in conformity with this view it is noticeable 

 that it is only those animals (mammals) which have a well-developed spirally wound 

 cochlea that show the inferior corpora quadrigemina as distinct prominences. In 

 nearly all vertebrates below mammals there are merely corpora bigemina, and these 

 seem mainly to represent the anterior pair of the quadrigemina of mammals. As 



Fig. 78. SECTION ACROSS THE MID-BUAIN, THROUGH THE SUPERIOR CORPORA QUADRIGEMINA. 

 Magnified about 3 diameters. (E. A. S. ) From a Photograph. 



Sy., aqueductus Sylvii ; c.p. , commissura posterior ; gl.pi., glandula pinealis ; c.q.a., grey matter of 

 one of the superior corpora quadrigemina ; c.g.m., corpus geniculatum mesiale ; c.g.L, corpus genicu- 

 latum laterale ; tr. opt., tractus options ; p.p., pes pedunculi ; p.l.b., posterior longitudinal bundle ; 

 fi., upper fillet ; r.n., red nucleus ; n.III, nucleus of third nerve ; ///, issuing fibres of third nerve ; 

 I. p.p., locus perforatus posticus. 



already mentioned, this anterior pair is chiefly connected with the optic nerves and 

 therefore with the visual sense. 



The tipper or anterior quadrigeminal bodies of man have been carefully 

 investigated by Tarfcuferi. Most externally or uppermost is a thin layer of superficial 

 neuroglia, containing no nerve-cells or fibres, but only fine stellate glia-cells and 

 the ends of glia-fibres which radiate from the central canal (aqueduct) towards the 

 periphery. Excluding this neuroglia-layer, and also the central grey matter around 

 the Sylvian aqueduct, Tartuferi distinguishes four strata in vertical sections. 



