. Journal of anatomy. head isthickened for a short distance, forming with the ectoderm of the uppermargin of the oral plate the primordium of Rathkes pouch (). Trans-verse sections show that in its cephalic portion the pouch is widely openon its ventral side, while its dorsal wall is closely applied to the di-encephalic floor. The pouch is, however, closed in its posterior portionand is bifid at its caudal extremity. The small pre-oral gut fits into thebifurcation of the pouch so that in the middle line its entoderm is incontact with the floor of the diencephalon, whilst on either side it
. Journal of anatomy. head isthickened for a short distance, forming with the ectoderm of the uppermargin of the oral plate the primordium of Rathkes pouch (). Trans-verse sections show that in its cephalic portion the pouch is widely openon its ventral side, while its dorsal wall is closely applied to the di-encephalic floor. The pouch is, however, closed in its posterior portionand is bifid at its caudal extremity. The small pre-oral gut fits into thebifurcation of the pouch so that in the middle line its entoderm is incontact with the floor of the diencephalon, whilst on either side it isseparated therefrom by the lateral branches of Rathkes pouch. Thewall of the pouch consists of several layers of columnar cells. The Development of the Hypophysis Cerebri, etc., in Marsupialia 199 The floor of the diencephalon is depressed to form the primitive in-fundibular recess, whose dorsal limit is indicated by a slight horizontalridge on the inside of the diencephalon. No infundibular process is Fig. 14.—Stage I. Trichosurus vidpcida (1, a, 01). Median longituilinalsection through the hypophysis and pocket. Si. 2-4-4. Dien., diencephalic floor; , oral plate ; , Kathkes pouch: , Seessels pocket. Stage II. 7 mm. (Embryo a 97).—In this stage the limits ofRathkes pouch are clearl}^ indicated by lateral grooves. The pouch isstill widely open anteriorly, but its opening has narrowed roof is thick, its posterior closed portion is quadrilateral in transversesection, and its caudal extremity is slightly bifid. The infundibular depression is relatively wide anteriorly, but becomesnarrower posteriorly, indicating the form and position of the infundibularprocess. A small rounded diverticulum situated caudal to the opening of Rathkespouch represents the degenerating remnant of Seessels pocket. Stage III. 7-5 mm. {Embryo XIX. 04).—The opening of Rathkespouch has narrowed so as to form a short, wide duct, while the
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectanatomy, bookyear1867
