THE CEREBRUM, AND ITS FUNCTIONS. 



745 



lutions of the Hemispheres, especially those of the middle lobe. [Fig. 189*, 

 a, c. ED.] This commissure is particularly large in those Marsupials in which 

 the Corpus Callosum is deficient. The Posterior commissure is a band of fibres 

 which connects together the Thalami Optici ; crossing over from the posterior 

 extremity of one to that of the other. [Fig. 194 J, p. c. ED.] Besides these, there 

 are other groups of fibres, which appear to have similar commissural functions, 

 but which are intermingled with vesicular substance. Such are the soft commis- 

 sure, which also extends between the Thalami ; the Pons Tarini, which extends 

 between the Crura Cerebri; and the Tuber Cinereum, which seems to unite the 

 optic tracts with the thalami, the corpus callosum, the foruix, &c., and to be a 

 common point of meeting for several distinct groups of fibres. Of the longitudi- 

 nal commissures, some lie above, and others below, the Corpus Callosum. Upon 

 the transverse fibres of that body, there is a longitudinal tract on each side of the 

 median line, which serves to connect the convolutions of the anterior and pos- 

 terior Cerebral lobes. Above this, again, is the Superior longitudinal commissure 

 [Fig. 194J ED.], which is formed by the fibrous matter of the greater convo- 

 lutions nearest the median plane on the upper surface of the Cerebrum, and which 

 connects the convolutions of the anterior and middle lobes with those of the 



[Fig. 194 



This figure has been introduced with the view of assisting the student in his study of the relations of the 

 inferior longitudinal commissure or fornix, which may he described as commencing in the centre of the thala- 

 mus nervi optici (L), proceeding from thence to the base of the brain, where it suddenly bends upwards and 

 forwards, forming by this turn the knuckle (B), which is called corpus albicans or mammillare. This body 

 receives a few fibres (A) from the locus niger (6) in the crus cerebri (5), running forward from thence towards 

 the anterior commissure, receiving fibres from the convolutions at the base of the brain, crossing and as it were 

 kneeling upon the anterior commissure (s), and, ascending towards the great transverse commissure, forms 

 the anterior pillar of the fornix (c), receiving fibres in its course from the under and front part of the anterior 

 lobes, and thus forming the septum lucidum (D) ; running back from thence, passing in its course backwards 

 over the thalamus nervi optici (L), it spreads laterally, constituting that portion which is called the body of 

 the fornix (E) : descending again at the back part of the brain, it forms the descending or posterior pillar of the 

 fornix tcenia hippocampi (F), some of its fibres running back to be connected with the posterior lobes (i) ; others 

 crossing the projection called hippocampus major (G), to be connected with the middle lobe, and others again 

 passing over the pes hippocampi (H) to be connected with the anterior portion of the middle lobe. Thus does 

 this commissure connect different portions of the convoluted surface of the brain together, which are inferior 

 to the great transverse commissure, and on the same side of the mesial line. A. Fibres of the inferior longitudi- 

 nal commissure, or fornix, from the locus niger. B. Corpus mammillare. c. Anterior pillars of inferior longitudi- 

 nal commissure, or fornix. D. Septum lucidum. E. Body of the fornix, or centre of the commissure. F. Tcenia 

 hippocampi, or descending fibres of the inferior longitudinal commissure. G. Fibres covering the hippocampus 

 major. H. Fibres covering the pes hippocampi, i. Fibres covering the hippocampus minor. K. Great trans- 

 verse commissure divided in the mesial line. L. Posterior cerebral ganglion, or thalamus. 1. Anterior corn, 

 missure. 5. Section of the crus cerebri. 6. Locus niger. 7. Anterior cerebral ganglion, or corpus striatum 

 partially scraped away. ED.] 



