THE CEREBRUM 497 



posteriorly. More anteriorly it is attached to the posterior 

 part of the lower edge of the septum pellucidum. Beyond 

 these attachments the upper surface of the body of the fornix 

 forms a part of the floor of the lateral ventricle, on each side, 

 and is clothed with ependyma. It presents a sharp lateral 

 edge, from under which the chorioid plexus projects into the 

 cavity of the lateral ventricle. The lower surface of the 

 body of the fornix rests upon the tela chorioidea of the third 

 ventricle (O.T. velum interpositum), a fold of pia mater which 

 separates it from the third ventricle and the two thalami. 



Columnce Fornicis (O.T. anterior pillars]. The two columns 

 of the fornix are two rounded strands which emerge from the 

 anterior end of the body of the fornix, and then, diverging 

 slightly, pass downwards anterior to the interventricular 

 foramen. Their lower ends sink into the grey matter on the 

 lateral walls of the third ventricle, and end at the base of the 

 brain in the corpora mamillaria. 



Each corpus mamillare has the appearance of being a twisted loop of 

 the corresponding column 'of the fornix, in which the fibres turn upon 

 themselves, and are then continued upwards and posteriorly into the 

 anterior tubercle of the thalamus. This appearance, however, is decep- 

 tive. In the interior of the corpus mamillare there is a nucleus of grey 

 matter. In this the fibres of the column end ; while the other fibres, 

 which seem to be continuous with the fornix fibres, take origin within the 

 nucleus. The strand, thus formed, is called the fasciculus thalamo- 

 mamillaris (O.T. bundle of Vicq d'Azyr) (Fig. 203). 



The connections which have just been described cannot be made out at 

 present, but at a later period the dissector will experience little difficulty 

 in tracing the column of the fornix to the corpus mamillare, and in dis- 

 playing the connection of this with the fasciculus thalamo-mamillaris. 



Crura Fornicis (O.T. posterior pillars]. The crura of the 

 fornix are flattened bands which diverge widely from the body 

 of the fornix. At first they are adherent to the under sur- 

 face of the corpus callosum, but soon they sweep downwards, 

 round the posterior ends of the thalami, and enter the inferior 

 horns of the lateral ventricles. There each crus comes into 

 relation with the corresponding hippocampus, and a portion of 

 its fibres become spread out on the surface of that prominence, 

 forming the alveus, whilst the remainder constitute the fimbria, 

 which has been described already (p. 494, Fig. 203). 



The transverse fibres of the fornix cross the lower surface 

 of the body and the anterior part of the interval between the 

 diverging crura. In the latter place they may be adherent 

 to the lower surface of the corpus callosum. On each side 



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