436 THE INTERNAL STRUCTURE 



a fan-like expansion, the ' corona racliata,' the edges of 

 the fan being directed, as Broadbent says, " forwards and 

 backwards, the surfaces inward and outward, but sloping 

 outwards, so that the outer surface looks downwards, and 

 is concave, the inner looks upwards, and is convex." 



On cutting across one of the Peduncles in front of the 

 Pons it is found to be separated into two layers of fibres 

 by a grayish black streak of ganglionic tissue, known as 

 the ' locus niger.'* Looked at from the under surface, the 

 most superficial stratum (that is, the under and anterior 

 stratum in the natural position of the Brain) is known as 

 the * Crusta^^ and is made up of wdiite fibres. It doubt- 

 less consists of the bulk of the outgoing fibres, w^hich 

 lower down are clustered together into the * anterior 

 pyramids ' of the Medulla, together with other fibres 

 terminating in * motor ' cell-groups in the Pons and 

 Medulla. Mixed with these, in all probability, are fibres 

 which suffice to connect the Corpus Striatum with the 

 Cerebellum through the intermediation of its * middle 

 peduncles.' The deeper stratum (that is the upper and 

 posterior parts of the Peduncles in the natural position 

 of the Brain), constituting what is known as the * Teg- 

 mentum,^ is not so white in colour, and seems to be 

 mainly composed of * ingoing ' fibres derived from the 

 Cord and Medulla. 



*' The Crusta and Tegmentum," Broadbent says, "can 

 be separated from each other for some distance upwards, 

 as they spread out to form the fan-like expansion spoken 

 of; but before they emerge from the central ganglia the 

 fibres of one sink in between those of the other, and they 

 become mixed together, so as to be no longer distinguish- 

 able." 



* Its colour being due to the abundance of pioment granules 



contained within the large nerve cells of this region. 



