112 DEVELOPMENT OF CEEEBRO-SPINAL SPACES IN PIG AND IN MAN. 



PLATE V. 



Fia. 10. Drawing of a pig embryo of 21 ram., in which an injection of diluted india ink was made into the central 

 canal of the spinal cord. The pressure employed was the highest obtainable from the syringe, yet below 

 the tension causing rupture. The specimen, after injection, was fixed, dehydrated, and cleared. The 

 slight extent of the periaxial spread of the carbon granules can be easily seen. Enlargement, 7 diameters. 



FIG. 11. Drawing of a pig embryo of 16 mm., in which an injection (under moderate syringe-pressure) of 0.5 per cent 

 solution of silver nitrate was made into the central canal of the spinal cord. The silver was reduced in 

 the sunlight, the embryo then fixed. After dehydration, the embryo was cleared in benzol and oil of 

 wintergreen. Enlargement, 7.5 diameters. 



Fio. 12. Drawing of a pig embryo of 13 mm.; into the central canal of the spinal cord a dilute solution of nitrate of 

 silver was injected under strong syringe-pressure. Reduction of the silver was accomplished by exposure 

 to sunlight; the embryo was then fixed, dehydrated, and cleared. Enlargement, 9 diameters. 



PLATE VI. 



FIG. 13. Photomicrograph of transverse section of a pig embryo of 18 mm. Specimen obtained from an embryo in 

 which the cerebro-spinal fluid was replaced by a 1 per cent solution of potassium ferrocyanide and iron- 

 ammonium citrate. After this replacement the embryo was kept alive for 65 minutes. The resultant 

 prussian-blue precipitate is not included in this photomicrograph. Enlargement, 13 diameters. 



Fia. 14. Drawing of blocked area in fig. 13, under higher magnification and including the resultant precipitate of 

 prussian-blue. The typical ependymal cells (epe) lining the fourth ventricle are shown on either side; 

 between them occurs the area membranacea superior (ams). The transit of the replacement fluid 

 through the membranous area and the spread through the adjacent mesenchyme are illustrated. En- 

 largement, 245 diameters. 



Fio. 15. Photomicrograph of transverse section from embryo pig illustrated in fig. 1.3. Section taken from more caudal 

 plane than that given in the former figure. The prussian-blue spread is not illustrated. Enlargement, 

 10 diameters. 



FIG. 16. Drawing, under higher magnification, of the rectangular area in fig. 15. The passage of the replaced solution, 

 as shown by the resultant precipitate of prussian-blue, through the area membranacea inferior (ami) is 

 here illustrated. The extension of the replaced fluid through the adjacent mesenchyme and the non- 

 penetration of the solution into the condensed mesenchyme are shown. Enlargement, 140 diameters. 



FIG. 17. Photomicrograph of sagittal section of a pig embryo of 18 mm. Specimen obtained from an embryo in which 

 the cerebro-spinal fluid was replaced by a 1 per cent solution of potassium ferrocyanide and iron-ammo- 

 nium citrate. After this replacement the animal was kept alive for 45 minutes. Fixed for 5 minutes 

 in 10 per cent fonnol containing 1 per cent hydrochloric acid; then over night in modified Benin's 

 solution (saturated aqueous solution of picric acid 75, formaldehyde 10, glacial acetic acid 10). Dehy- 

 drated by 2 and 4 per cent grades of alcohol; embedded in xylol-paraffin. Serial sections, stained by 

 hematoxylin and eosin. The resultant precipitate of prussian-blue has not been reproduced in the 

 photomicrograph. Enlargement, 8 diameters. 



FIG. 18. Drawing of blocked area in fig. 17 under higher magnification. The granules of prussian-blue are here repre- 

 sented by the blue stenciling. The transit of the fluid, as shown by the granules, into the periaxial 

 mesenchyme through the two membranous areas (ams and ami) in the roof of the fourth ventricle are 

 well shown. Enlargement, 35 diameters. 



PLATE VII. 



FIG. 19. Photomicrograph from a sagittal section of a fetal pig of 27 mm. The cerebro-spinal fluid in this specimen 

 was replaced by a 1 per cent solution of potassium ferrocyanide and iron-ammonium citrate; the fetus 

 was kept alive for 40 minutes; fixed in 10 per cent formol containing 1 per cent hydrochloric acid for 

 15 minutes; then over night in modified Bouin's solution; dehydrated by 2 and 4 per cent grades of 

 alcohol; embedded in xylol-paraffin. The prussian-blue granules are not represented in this photo- 

 micrograph. Enlargement, 8 diameters. 



FIG. 20. Drawing of squared area in fig. 19. The center of the field is occupied by the optic nerve; around it the 

 developing extrinsic optic muscles are shown. The precipitate of prussian-blue occurs in the perineural 

 mesenchyme. Enlargement, 190 diameters. 



FIG. 21. Photomicrograph of rectangular area in fig. 19. The passage of the ferrocyanide solution into the sinus 

 transversus (str) is represented by the precipitated blue granules. Enlargement, 133 diameters. 



FIG. 22. Photomicrograph of a transverse section of a pig embryo of 23 mm. The cerebro-spinal fluid was replaced 

 in this embryo with a 1 per cent solution of potassium ferrocyanide and iron-ammonium citrate. The 

 embryo was kept alive for 50 minutes and was then fixed over night in 10 per cent formol containing 1 

 per cent hydrochloric acid. The granules of prussian-blue are not shown in this reproduction. Enlarge- 

 ment, 13 diameters. 



Fio. 23. Drawing of squared area in fig. 22. The area membranacea superior (ams) is shown, surrounded on either 

 side by tufts of the chorioid plexus (chp) and the typical ventricular ependyma. The transit of the 

 solution is shown, as represented by the resultant granules, through the area, with the subsequent spread 

 into the periaxial mesenchyme. Enlargement, 125 diameters. 



