THE TEGMENTUM AND THE PEDUNCLE OF THE MIDBaAIN. 



297 



the region of the corpora quadrigemina, let us study a section through the 

 anterior quadrigeminal bodies, the structures of the tegmentum, and the 

 pedunculi cerebri (see Fig. 192). 



Taking bearings from structures already known, note on each side ex- 

 ternally the pulvinar thalami, from which the optic nerve appears to come. 

 The corpus geniculatum latcrale seems to be inclosed in the course of the 



Fig. 191. — Showing the transition from the interbrain to the midbrain. The 

 section is from the brain of a dog and is about one millimeter posterior to that 

 shown in Fig. 177. Compare carefully the series represented in Figs. 169, 176, 

 177, and 191. Note: the Commissura post., whose most anterior fibers are 

 severed; the stratum sonale, fibers from the anterior quadrigeminal bodies into 

 the opticus; the pulvinar; the Nuc. ventralis thalami; the Superior lemniscus 

 or fillet (Obere HcMHfe), which is nearer the median line and larger than in 

 Fig. 177; the fasciciilKS retroflexiis, which has passed off from the ggl. haben- 

 uIee; the most anterior fibers of the inferior lemniscus {Uiit. Schleife), which 

 arises from a gray nucleus that merges into the median marrow of the corpora 

 quadrigemina; the most anterior fibers of the oculo-motorius (Radices N. Ill) ; 

 the posterior lotujituditial fascicle, which arose in the preceding section by a 

 few fibers from its nucleus, now grown larger; the optic radiation {Selistrahl- 

 ung), which is the pedicle of the anterior quadrigeminal body and of tire cor- 

 pus geniculatum laterale. The large nucleus, designated Nucl. ventr. thalami 

 gradually merges below into the corpus geniculatum mediale. Note also the 

 decussation between the cornua Ammonis and the position of the fornix longus. 

 In the pes pedunculi the stratum intermedium composed of fibers from the 

 lenticular ganglion in the regio subthalamica. 



