122 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



month only one small fasciculus, which has become medullary. 

 It lies externally, and is not shown in the cut. It emerges 

 probably from the ansa lenticularis. 



In Fig. 72 we have a picture which represents most of the 

 structures which can be seen in a section just behind the ante- 

 rior quactrigemmal body. This cut is prepared from specimens 

 at various periods of development. We will make use of it for 

 a review of to-day's lecture, and look up the following important 

 points : 



1. Hoof of mid-brain : Anterior quadrigeminal body; from 



FIG. 71. 

 Diagram of a sagittal section through the thalanms and the corpora quadrigemina. 



Bindtarm, Sup. cerebellar pedunc. [Itiulirnliumlel, Tegmeutal fasciculus. 



Viq. d'Azyr. JS., Viq. d'Azyr's bundle. 



this there arises dorsad the brachium to the optic nerve, ventrad 

 the deep marrow, the decussation of the latter over the aque- 

 duct, the central gray matter surrounding the aqueduct. On the 

 outer border of the central gray matter a small nucleus, unmen- 

 tioned before, whose vesicular cells Avill be found in the same 

 relative position throughout the entire mid-brain. From it 

 arises a slender bundle of fibres which, progressively increasing 

 in size, passes downward to the pons and there associates itself 

 with the emerging fibres of the trigeminus. It is the descend- 

 ing root of the fifth nerve. 



2. Tcgmentum : In the ventral portion of the central gray 



