OOO ) 



boiu'hood of tlie floor fold of I lic ni-iuiary fonunen Moiiroi (not in 

 tlic foramen itself). 



The ahove-nienlioned a|)|teiidices of llio linnen of die nndl»rain 

 have already become nidiiiicnlai-v. The characlerislic enclosure of 

 llic ceivhral pari of (he hypophysis by Ihc plia:'yn,ueal pari: is mei. 

 w idi here in a similar way as in odier orders of mannnals. The 

 lamella of die cerebelbim has grown thicker. Of the longitndijial 

 grooves, it is only the snlens dorsalis medialis and the sulcus 

 mediamis dorsalis that are well marked on the innei- surface. On 

 the onter surface the ridges and grooves have been almost entirely 

 flattened (tut. The |)OSterior longitudinal bundle, the spinal root of 

 the trigeminus and the lower olive form already distinct j)rominen- 

 ees. The choi'ioid plexus of the fourth ventricde has already invagi- 

 iiated itself considerably. The dilferences i]i level of the fossa 

 rhomboidea have already a little more flattened out. The sulcus 

 intermedins is lacking, the sulcus linutans is distinct. The labial 

 grooves have become flatter. 



The next-following changements may be briefly summarised as 

 follows : 



<i. The hemis[)heres sliow^ a deep groove eorres|)onding to the thalani- 

 encephalon, vallis diencephalica. The medial \\'all of each hemisphere 

 shows on horizontal section three ridges projecting towards the lumen 

 of the ventricle, which we will denote by R, S and T in tlieii- 

 order from befoi'e backwards. Between S and 7' w^e find, followinü' 

 iij) the series in a basal direction, a great dimijintion in the ddckncss 

 of the ventricular wall (part d). In this thinner jmrt and much 

 nearer to »S' than to 7' the formation of the chorioid fissure occurs 

 and the invagination of the plexus chorioideus ventriculi lateralis. aS' 

 and li coalesce more and more. iMeanuhile from the lower posterioi* 

 part of the wall of the hennspherical ventricle the broad ridge of 

 the caudate nucleus arises. The lateral ventricular wall shows only 

 a very slight thi(dveiuiig, resp. elevation A' in its [)osterior part, 

 wdiich at higher (i. e. moi*e parietally situated) levels, together with 

 the caudate nucleus marks a narrow slit and coalesces with the 

 caudate nucleus at lower levels. Between the caudate Jiuclens and 

 the ridge 7' there is a fold, which ma\ be denoted by r. A very 

 shallow^ pronujience /^ is also shown by the lateral wall in its 

 most antei'ior part. The further the sei-ies is followed in a basal 

 direction the moi-e coJispicuously a short anterior portion is mai-ked 

 off on the medial hrmispherical surface of the \allis diencephalica, 

 which poi'tioii is nol contiguous w idi the llialameiic(>phalon, but is 

 separated IVoiu the cori-espoiKling part of the other hemisphere by 



23* 



