THE EMBRYONIC PIA
Abstract
THE BAssistant Physician Hospital; and InstructorEMBRYONIC CLARENCEDirector in Psychiatry, ofPIA. B. FARRAR,the Johns Laboratory, Hopkins Sheppard-Pratt University.The encephalon rived from theis essentially epiblast in thean ectodermal organ, being dedeveloping embryo. Very early,however,the surroundedas soon as the become differentiated,sheath, dura cordcerebral thevesicle appears and ectodermal organ iswhich by and into arise later the a This developexamining chick. extending and when is comfrom its to the mesomesoblasta mesodermaltwo membranes,-the ment and differentiation cross-section As they pletely original formation blastic soon as the the finally dorsally, of the medullary underlying .coalesceand the pia-arachnoid. can be well followed region ridges mesoblast are the in an formed pushes neural layer, structures. in front as with muscular, it follows of the relations. mesoblastic into whose the the the latter to the tube, shutting epiblast This the earlyembryonic begin them, the which common latter it off goes enclosingto withform thesurrounded connection of sheath theby a mesoblastic superficial integumentalis continuouswhich gives rise to the vascular, systems, but becomes narrow sally, mata The to the mentary derivatives nective-tissueand other mesodermal the neural tube dorpresents (Plate sheath formation VI.) lying of adjacent the rudiare con-? which as a delicate scheaccompanyingat the recallpoint structure. clearly portionof closure these of