90 



of the deepest part of the tectum mesencephali . At the crown 

 of the arch which the optic lobe presents in section, the fi- 

 bres are seen as gre^it horizontal bundles interrupted at al- 

 most perfectly regular intervals by small groups of vertical 

 fibres. The two lateral halves are united by a strong commis- 

 sure just dorsal to the aqueduct of Sylvius. Pig. ?0, s. m. p. , 

 represents these features in a transverse section. 



Traced laterally, the fibres of the stratam meduUare pro- 

 funda™ are found to pass into the base of the midbrain in tvo 

 somewhat clearly marked divisions. The outer division takes 

 a large number to the lateral surface (Pig. ?0,e.l. ); while a 

 markedly smaller group passes downward nearer the median line 

 for a ventral decussation (Pig. 80, i. 1. ). Tne inner division 

 is composed of those fibres lying nearer to the central gray 

 niatter from the outset. Some of these have but a short course 

 downward and out^rari, but the great mass of fibres continues 

 near the median line as a series of intercrossing bundles which 

 are destined to decussate ventral to the aqueduct of Sylvius 

 (Pig.20.e.m.,i.m. ). 



The fibre-system composing the stratam medullare ppofun- 

 dura must be indeed important in the economy of the brain. Into 

 this system we have traced fibres from the cord and oblongata, 

 fibres from the optic nerve, and from the neurones of the tec- 

 tum mesencephali itself, 'fie will subsequently have occasion 

 to point out that a great tract sweeps into it from the inter- 

 brain as a relay in the olfactory apparatus. Pibres are also 



