210 D. DAVIDSON BLACK 



MACROSCOPIC DESCRIPTION OF THE BRAIN 



For the sake of convenience in description the following terms 

 have been made use of. Those structures which together form 

 that portion of the brain anterior to the pineal region are col- 

 lectively spoken of as the primary forebrain vesicle. The pri- 

 mary forebrain vesicle is further subdivided into an anterior cere- 

 bral vesicle or cerebrum, and a posterior thalamus or thalamic 

 mass. 



Primary forebrain vesicle 



From above: As seen in figure 48, this region appears as a 

 large unpaired vesicle having a smooth arched roof which extends 

 caudad to a point immediately in front of the corpus pineale. 

 At no point does it arch over the posterior brain segments. 



From the side: In the lateral line is here seen a very distinct 

 sulcus passing in a circumferential manner around the cerebral 

 vesicle. Its origin is hidden posteriorly in a deep fissure which 

 exists between the basal portion of the primary forebrain vesicle 

 and the brain stem. The relation of this sulcus may be seen by 

 comparing figures 48, 49 and 50. It sharply marks off the smooth 

 bulging roof from the thickened and somewhat furrowed base. 



From below: The general configuration of the inferior surface of 

 the primary forebrain vesicle is well illustrated in figure 50. It 

 is seen to be divided by a quite marked Y-shaped furrow into 

 two paired posterior lobes and a single azygos anterior lobe. 

 This furrow cannot be compared with any sulci appearing on 

 the surface of the normal cerebral hemisphere. It is apparently 

 only the result of a mutual adaptation between the cerebral 

 vesicle and the floor of the skull cavity. Smaller secondary fur- 

 rows are seen on each of the lobes but the direction in each case 

 is always at an angle to the main Y-shaped furrow. Apparently 

 these very shallow sulci are due mainly to the presence of blood 

 vessels. In the azygos anterior lobe a small fossa is seen directly 

 in front of the diverging limbs of the Y-shaped principal furrow. 



There is no appearance whatever of olfactory lobes, optic 

 nerves or tract, infundibulum, or in fact of any structure nor- 

 mally appearing in a basal view of this portion of the brain. 



