348 



ANATOMY IN A NUTSHELL. 



creases in size as the corpus callosum increases. The anterior fibers of the an- 

 terior commissure (pars olfactoria) connect the olfactory bulbs of opposite sides 

 and in man is very small, but in osmatics it is large, being twice as large as the 

 posterior portion or hemispheral bundle of fibers. This anterior portion is large 

 in fishes. The posterior portion of the anterior commissure connects the tem- 

 poral lobes and the amygdalae nucleus of opposite sides. The middle fibers 

 pas through the olfactory bulb of one side to the temporal lobe of the opposite 

 side. Thus we may have a lesion on one temporal lobe producing loss of smell 

 of the opposite side of the nose called crossed anosmia. 



The middle or soft commissure is gray; it is very delicate, though some- 

 time- it is double. It connects the two optic thalami, which takes place about 



PLATE CLXVI1I. 



EPIPHYSIS 



CORPORA QUAORIGEMINA 



5TH VENTRICLE 



IN 

 SEPTUM LUCIDUM 



FORAMEN Of MONRO 



HYPOPHYSIS 



A Sagittal Section of the Brain. 



the fifth month of intra-uterine life. It is not really a commissure as no fibers 

 pass from it from one side of the brain to the other. 



The posterior commissure is white and is situated behind the upper end of 

 the aquedud of Sylvius. It forms part of the posterior boundary of the third 

 ventricle. The pineal gland is just above and slightly posterior to it. Most 

 of the fibers of this commissure are a continuation of the fibres of the fillet, 

 which after decussation, pass through the optic thalamus into the corona radiata 

 of the opposite side. The anterior fibres pass from the root of the pineal gland 

 to the nucleus of the trigonum habenulse on one side and the nucleus of the 

 third nerve of the opposite side. 



The fornix is composed of Longitudinally arched bundles of fibers. It 



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