XXXIII] THE MID-BRAIN AND INTER-BRAIN 265 



the p. c. q. the elongated medial fillet ; this forms the 

 ventral boundary of the tegmentum. 



The decussating sup. cer. peds. forming a large 

 round whitish mass in the mid-region of the teg- 

 mentum. 



The central grey mass of the p. c. q., and with a 

 band of white fibres in its ventro-lateral region (fibres 

 of the lateral fillet), spreading into it and over it 

 laterally (cp. Demons. 1), and in a thin line medially. 



The nucleus of the 4fth nerve, a group of large nerve 

 cells in the grey substance dorsally of, and in the post, 

 long, bundle. 



6. Section at posterior third of the p. c. q. and anterior part of 

 pons (dog). Note: 



The post. corp. quadrigemina do not meet in the middle line; a 

 thin membrane attached about half-way up the p. c. q. covers in the 

 aqueduct. 



The interpeduncular ganglion, a round mass situated in the middle 

 line between the pedes, dorsal to the pons fibres ; grey substance 

 corresponding to this will also be seen in the corresponding sections 

 in man ( 3 and 5). 



7. Section at the anterior third of the p. c. q. and just in front of 

 the pons (dog). The membrane of the roof of the aqueduct starts 

 nearly from the dorsal limit of the p. c. q. ; the lateral fillet is no longer 

 seen ; the dorso-lateral surface of the p. c. q. has a cap of fibres ; the 

 4th nerve nucleus stretches ventrally between the strands of the 

 p. 1. b. ; the lateral edge of the median fillet extends a little dorsally ; 

 the decussation of the s. c. ped. is only seen in the ventral part of the 

 section ; the interpeduncular ganglion is free on the medial ventral 

 surface. Note : 



The pes, ventrally and a little laterally ; it is much smaller than 

 in man, cp. 9. 



Between the pes and the fillet, the rather thin line of grey 

 substance with distinct nerve-cells, the substantia nigra. 



