CHOROID PLEXUSES 



f03 



The under surface of the velum interpositum rests on the inner parts of the optic 

 thalanii, and between the hitter it is phiced directly over the third ventricle, where 

 it is covered by a layer of ei)ith('lium continuous with the lining of that cavity, V)ut 

 discontinuous Avith the epitheliuiu of the lateral ventricles, except at the foramina 

 of Monro. 



The choroid plexuses extend from the extremity of the descending cornu of 

 each side to the foramen of Monro where they become continuous with one another 

 through the foramen commune anterius. From the junction of the two plexuses 

 a pair of small vascular fringes pass backwards on the under surface of the velum 

 interpositum in the middle line, and depend into the cavity of the third ventricle, 



Fig. 420. — Horizoxtal Section of the Ceeebeal Hemispheres. 



(From a mounted specimen in the Anatomical Department of Trinity College, Dublin.) 



(The fornix has been reflected to show the velum interpositum.) 



.( XTERIOR 

 PILLARS 

 OF FUR MX 



POSTERIOR 



PILLARS 



OF FORNIX § 



Straight sinus 



CFRF- 

 RELLVM 



CORPUS 

 CALLOSUM 

 (in section) 

 SEPTUM 

 LUCID UM 



FIFTH 

 VENTRICLE 



TJENIA SEMI- 

 CIRCULARIS 

 OPTIC 

 THALAMUS 



Velum 

 interpositum 



Choroid p/exus 



FIMBRIA 



HIPPOCAM- 

 PUS MAJOR 



EMIXEXTIA 

 COLL A TER- 

 ALIS 



- HIPPO- 

 CAMPUS 

 MIXOR 



constituting the choroid plexuses of that cavity (fig. 414). The anterior choroid 

 artery enters the choroid plexus at the termination of the descending cornu; other 

 smaller arteries are supplied to the plexus from behind, and are derived from the 

 posterior cerebral artery. 



Dissection. — The student should divide the splenium of the corpus callosum in tlie middle 

 Hue, and remove the ]iortions of tlie hemispheres which lie ))osterior to tlie great transverse 

 fissure ; they will readily separate at the fissure, and break off at the extremities ol' tlie temi)oral 

 lobe.s. This operation should be conducted with gentleness, as the walls of the third ventiicle 

 are very prone to become unduly divaricated by this di.ssection. The \y,\rt removed should be 

 re-examined, as the relations between the fissures and hip|)ocampi can be studied to great 

 advantage at this stage. The cavity of the third ventricle may now be displayed by raising the 



