777 /; CEREBRAL HEMISPHERES 



915 



ventrocaudad to form the genu ("knee"), including an interval, between the two 

 limbs, which is flanked on both sides by a thin lamina (hemiseptum) and bounded 

 ventrad by the fornix, constituting a closed cavity, the pseudocele. The recurved 

 ventral part of the genu tapers into a thinner, beak-shaped part, the rostrum. 

 The rostrum is joined to the lamina terminalis, fronted of the anterior commissure, 

 by a thin lamina, the copula (lamina rostralis; lamina baseos alba). 



An arched structure composed of longitudinal h'bre bundles comes to view 

 in front of and below the junction of the splenium with the body of the corpus 

 callosum, proceeds frontoventrad with its convexity frontad, to sink from view in 

 the substance of the hypothalamic gray at a point just caudad of the anterior 

 commissure. This white arched bundle is the fornix. Between it and the corpus 

 callosum, rostrum, and copula stretches a thin, translucent lamina of nerve 

 tissue the hemiseptum. The hemisepta of the two sides together have usually 

 been termed the septum pellucidum, while the enclosed narrow cavity is called the 

 pseudocele or fifth ventricle. The subjacent parts revealed in this section have 

 already been described; the morphology and internal relations of the corpus 

 callosum, fornix, and hemiseptum will be described at a later stage. 



OCCIPITAL F. 



FIG. 671. Principal fissures and lobes of the cerebrum viewed laterally. 



The cerebral hemispheres together, as viewed from above or dorsally, appear 

 as two symmetrical masses in close apposition, conforming in outline to that of 

 the cranial cavity, which they so nearly fill. The frontal extremities or poles are 

 massive and rounded, preponderatingly so in comparison with the brains of any 

 related primate species. The occipital poles are each more pointed but expand 

 frontad into the widest part of the cerebrum the parietal lobes. The cerebral 

 hemispheres or, briefly, the hemicerebra are partially separated from each other 

 by the intercerebral cleft or great longitudinal fissure (fissura lonyitudinalis cerebri}, 

 into which fits a fold of the dura the falx cerebri. By means of a large com- 

 mi.ssural band of white fibres the corpus callosum the cerebral halves are joined 

 together in the depths of the intercerebral cleft. All adjacent parts of the brain 

 are overlapped by the ponderous cerebrum so as to entirely conceal the thalamic 

 portion and the mid-brain, while the occipital lobes overlap the cerebellum with 



