THE CORPORA QUADRIGEMIXA. 



771 



therefore named the Jurinna nn.fnlrifj'--miiifi. The ventral part of the Lamina 

 mid-brain is much larger, and constitutes the crura < erebri. The geniina. 

 lamina qiiadrigemina is separated from the crura in the middle by 

 a oanal _ the aqufflurt of .Si.//o/x ; but on each side it is united with Aqueduct of 

 the tegmentum. 



The CORPORA QUADRIGEMIXA (fig. 277) are four prominent bodies, Qjjjjjjj 

 an upper and lower pair, which are separated by a crucial groove, bodies: 

 The superior, or anterior, eminence (h) is the larger, and is rather oval anterior, 

 in shape. The inferior, or posterior, (t)lB smaller, but more prominent, posterior. 

 and rounded ; it is also whiter in colour than the upper one. From 

 the outer side of each quadrigeminal body a white band, brachium Brachia. 

 (fig. 281) is continued outwards and forwards : the upper brachium 

 paWs into the optic tract ; while the lower band sinks Ijeneath a 

 small but well defined oval prominence, which is placed between 

 the cms cerebri and the optic thalamus, and is named the -intmtfil 

 i.-fiinilntr body (fig. 281). 



The quadrigeminal bodies are small masses of grey substance, 



inf. quad, body aqueduct of Sylvius 



X X~~ ; '^~~\ lamina cpadriaemina 

 jreij matter of /. 

 aqueduct ^j2. 



fillet 4-1 J^J/_ \\tcgnicnfcum \ 



prt^-iAir-S ft //S_ 8 ub 8 tantia[ CPU- 



crusta 



FIG. 280. TRANSVERSE SECTION OF THE LOWER PART OF THE'MIDBRAIN. 



covered by a white layer. From the grey matter of the upper one 

 fibres of the optic tract take origin. 



Behind the quadrigeminal bodies are seen the superior peduncles 

 of the cerebellum (fig. 277, /) ; with the valve of Yieussens, or 

 superior medullary velum (A'), between them. Issuing from beneath 

 the transverse fibre* of pons, and arching over the cerebellar 

 peduncle, is an oblique, slightly raised band named the fillet Below 

 (fig. 286 /, p. 782), which disappears under the lower quad- tiufmie? is 

 rigeminal body and its brachium. seen. 



The FILLET is a M'hite fibrous tract which appears in sections of Fillet: 

 the pons between the recticular formation and the deep transverse 

 fibres (fig. 267^, and fig. 280). It is formed mainly by fibres ori s in > 

 continued upwards from the anterior and lateral columns of the 

 same side of the spinal cord, by others from the nuclei of the 

 posterior columns (cuneate and gracile) of the opposite side of the 

 bulb, and, in its lateral portion, by fibres connected with the cochlear 

 portion of the eighth nerve. At the upper edge of the pons the 

 outer part of the fillet becomes superficial, and curving round the ending of 

 tegmentum (fig. 280), passes to the quadrigeminal bodies, particularly Jn|rt!5ai 

 to the posterior, in which many of the fibres are lost, while others part, and 



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