DEVELOPMENT OF THE CHOROID PLEXUS 85 



jection apparatus. One millimeter plates were used and ever}- 

 other section drawn except in the region of the foramen inter- 

 ventriculare, where half millimeter plates were used and every 

 section drawn. The epiphyseal region was modeled at a magni- 

 fication'of 100 diameters. Millimeter plates were used and every 

 section was drawn. 



Embryo H 91 was obtained from an aborted ovum 50 x ;U 

 X 30 mm. presented by Dr. G. C. Dittmann of Chicago, whose 

 data indicate a clinical pregnancy of 60 days. The ovum was 

 left unopened in physiological salt .solution for 10 hours, then 

 opened and fixed in an S per cent .solution of formaldehyde, 

 neutralized with magnesium carbonate. It measured 27.8 mm. 

 crown-rump length after fixation in formalin and showed a 

 shrinkage of 13. () per cent after imbedding in paraffin. It was 

 stained in bulk in borax carmine and on the slide with orange 

 G. It was cut in 20m sections, and modeled at a magnification 

 of 40 diameters. Millimeter plates were used and every fifth 

 section was omitted. 



Embryo H 41 was obtained fiom an u\uni of 71 x 39 x 32 nun., 

 presented by Dr. L. A. Beaton of Chicago. The chorion was 

 opened and the entire ovum fixed in formalin. The crown- 

 rump measurement of the embryo after fixation was 32.1 mm. 

 and it showed a shrinkage of 10 per cent after imbedding in 

 paraffin. The staining was the .same as that of H91. Tliis 

 embryo was sectioned 20m in paraffin, and modeled at a magni- 

 fication of 25 diameters. ^Millimeter plates were used and every 

 other section was drawn. The region around the foramen of 

 Monro was modeled at a magnification of 100 diameters; 2 mm. 

 plates were used and every section was drawn. 



Two points in the technical procedure are to be emphasized 

 because they are in large measure responsible for the exception- 

 ally good preservation of the form relations of the delicate roof 

 plate of the brain. Both of the older embryos (H 91 and H 41) 

 had the cranial cavity opened by an incision in the line of the 

 sagittal suture. Distortions due to unequal shrinkage of the 

 brain and overlying structures were thereby in great measure 

 avoided. All three were passed from 95 per cent alcohol to 



