t4i6 



A MANUAL OF ANATOMY 



The floor, which is sloped downwards and forwards, is formed 

 by the structures which lie within the interpeduncular space at 

 the base of the brain, these being as follows, from behind for- 

 wards: the locus perforatus posticus, the corpora mammillaria, 

 and the tuber cinereum, with the upper end of the infundibulum. 

 The tegmenta of the crura cerebri enter, to a certain extent, into 

 the floor posteriorly, and the optic commissure lies across it 

 anteriorly. Above the optic commissure the floor presents a depres- 

 sion, called the optic recess, and behind this there is another 

 depression or diverticulum, called the infundibular recess. The 

 latter forms the upper part of the infundibulum which leads to the 

 posterior lobe of the pituitary body. 



The lateral wall is slightly convex, and is formed, for the most 

 part, by the inner surface of the optic thalamus, which has a thick 



Suprapineal Recess 



Posterior Comu 



Anterior Cornu 



- Foramen of 

 Monro 

 Position of Anterior 

 Commissure 



Recess 

 bulum 



Fourth Ventricle 



Lateral Recess of Fourth Ventricle 



Fig. 597. — Drawing of a Metal Cast of the Ventricles of the 

 Brain of an Adult (Right Lateral View) (Retzius). 



covering of grey matter. Towards its centre it presents a furrow, 

 which leads from the foramen of Monro in a backward direction 

 towards the upper opening of the aqueduct of Sylvius. This groove 

 is called the sulcus of Monro. At the upper part of the lateral wall 

 there is a delicate band of white fibres, called the stria pinealis or 

 medullaris, which represents the dorsal portion of the stalk of the 

 pineal body, and passes to the anterior pillar of the fornix. Con- 

 necting the two lateral walls (optic thalami), in front of the centre 

 of the ventricle, there is a fragile band of grey matter, called the 

 middle or soft commissure. At the anterior part of the lateral 

 wall the corresponding anterior pillar of the fornix passes down- 

 wards and backwards. 



The anterior boundary is formed inferiorly by the lamina termin- 



