744 



OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



other; the latter uniting the different parts of the same Hemisphere. Of the 

 transverse commissures, the Corpus Callosum is the most important. This 

 consists of a mass of fibres very closely interlaced together ; which may be 

 traced into the substance of the hemispheres on each side, particularly at their 

 lower part, where their connections are the closest with the Thalami Optiei and 

 Corpora Striata. It is difficult, if not impossible, to trace its fibres any further; 



[Fig. 194J. 



This figure represents longitudinal fibres placed above the great transverse commissure corresponding with 

 those which we have just observed below it the superior longitudinal commissure. The relations being more 

 simple than those of the inferior commissure, are simply designated by the letters s L, s L. They are traced, 

 ascending forwards, from the locus quadratus, which is anterior to the fissura Sylvii, and then, curving back- 

 wards and winding round the front of the great transverse commissure (p), receiving fibres from all the con- 

 volutions at the upper and sides of the hemispheres, winding round the posterior extremity of the same com- 

 missure, and terminating after crossing the fissura Sylvii, where it commenced in the locus quadratus at the 

 base of the brain. H. Spinal cord. J. Pituitary gland, just above which is the divided optic nerve. N. Letter 

 placed on the crus cerebri, and behind that root of the fornix which springs from the interior of the thalamus. 

 P. Great transverse commissure. S. Olivary ganglion, a. Olfactory ganglion, c D. Optic ganglia, c a. Cor- 

 pus mammillare, formed by the twist of the fornix. c m. Commissura mollis in the third ventricle, k. Optic 

 thalamus. o. Peduncle of the pineal gland : if this line is traced backwards, it will be found connected with a 

 dark rounded body, the pineal gland, which is lying on the anterior optic tubercle nates; if this line is traced 

 forwards, it will be seen joining the anterior pillar of the fornix, which has been turned down to show this 

 connection. The divided end of the fornix is turned towards us. p c. Posterior commissure, s. Taenia semi- 

 circularis joining the fornix at the same point. This letter is placed in the anterior cornu of the lateral 

 ventricle on the corpus striatum. This junction is very distinct in both the recent and hardened brain, 

 though the connecting fibres are too delicate to be done justice to in a woodcut. 4. Fourth ventricle. P. Iter 

 a tertio ad quartum ventriculum. c. Posterior commissure. ED.] 



but there can be little doubt that they radiate, with the fibres proceeding from 

 the bodies just named, to different parts of the cortical substance of the 

 Hemispheres. This commissure is altogether wanting in Fish, lleptiles, and 

 Birds; and it is partially or completely wanting in those Mammals whose 

 Cerebrum is formed upon the least complex plan the Rodents and Marsupials. 

 The Anterior commissure particularly unites the Corpora Striata of the two sides : 

 but many of its fibres pass through those organs, and radiate towards the convo- 



