116 DEVELOPMENT OF CEREBRO-SPINAL SPACES IN PIG AND IN MAN. 



PLATE XVI. 



Flo. 97. Photomicrograph of a transverse section of a pig embryo of 19 mm. Fixed in modified Bouin's fluid, dehy- 

 drated by 2 and 4 per cent grades of alcohol, and embedded in xylol-paraffin. Enlargement, 10 diameters. 



Flo. 98. Photomicrograph, under higher magnification, of the blocked area in fig. 97. The double condensations of 

 mesenchyme to form pia mater (pmc) and cerebral blastema (cbl) appear separated by a region of mesen- 

 chyme which is breaking down. This central area of mesencbyme, with the marked albumen-content, is 

 to become the arachnoid spaces. Enlargement, 133 diameters. 



Flo. 99. Photomicrograph of a transverse section of a pig embryo of 20 mm. Fixed in modified Bouin's fluid, dehy- 

 drated by 2 and 4 per cent changes of alcohol, and embedded in xylol-paraffin. Enlargement ,10 diameters. 



FlG. 100. Photomicrograph, under higher powers, of the blocked areas in fig. 99. The relations of the pial condensation 

 (pmc) of mesenchyme to the nervous system, as well as the infiltration of the arachnoid mesenchyme (sas) 

 with albumen, is reproduced. Enlargement, 133 diameters. 



FIQ. 101. Photomicrograph, under higher magnification, of the blocked area in fig. 22. The reproduction is included 

 here to show the double condensation (cbl) of mesenchyme which goes to form ultimately bone and pos- 

 sibly a portion of the dura. Enlargement, 132 diameters. 



FIG. 102. Photomicrograph of a transverse section of a pig embryo of 18 mm. The embryo was one in which the 

 cerebro-spinal fluid was replaced by the ferrocyanide solution. Subsequently the embryo was fixed in 

 10 per cent formol containing 1 per cent hydrochloric acid for a few minutes to precipitate the prussian- 

 blue. It was then transferred to modified Bouin's solution, dehydrated by 2 and 4 per cent grades of 

 alcohol, and embedded in xylol-paraffin. The granules of prussian-blue are not represented in this 

 figure. Enlargement, 10 diameters. 



FIG. 103. Photomicrograph of the squared area in fig. 102. The relation of the thinning mesenchyme in the arachnoid 

 areas to the caudal cranial nerves is shown. The granules of prussian-blue, scattered through the area 

 of thin mesenchyme (sas), are not reproduced. Enlargement, 40 diameters. 



FIG. 104. Photomicrograph of a coronal section of a tissue block which includes the meninges and cerebral cortex in 

 the region of the sinus sagittalis superior. The block was obtained from a fetal pig of 80 mm., fixed in 

 Zenker's fluid, and stained, after embedding in celloidin, by Mallory's technique for connective tissue. 

 Enlargement, 27 diameters. 



PLATE XVII. 



FIG. 105. Photomicrograph of a coronal section of a tissue block including cerebral cortex and meninges in the region 



of the sinus sagittalis superior. The block was obtained from a fetal pig of 10 cm., fixed in Zenker's fluid, 



and stained by Mallory's technique for connective tissue. Enlargement, 13 diameters. 

 FIG. 106. Photomicrograph of a coronal section, similar to that in figs. 104 and 105, except in that it was obtained from 



a fetal pig of 17 cm. The same technical procedures employed in the other specimens were used in this. 



Enlargement, 27 diameters. 

 FIG. 107. Photomicrograph of a similar section to those of the foregoing figures. The specimen was obtained from a 



fetal pig of 20 cm. and was treated in the manner outlined above. Enlargement, 20 diameters. 

 FIG. 108. Drawing of the cell pattern from the inner surface of the dura mater of a fetal pig of 5 cm. The specimen 



was prepared by the reduction of a dilute solution of silver nitrate in sunlight. The preparation was 



subsequently stained by hematoxylin. Enlargement, 190 diameters. 

 FIG. 109. Drawing of a preparation, similar to that of fig. 108, but obtained from the inner surface of the dura mater 



of a fetal pig of 75 mm. Enlargement, 285 diameters. 

 FlQ. 110. Drawing of a preparation, similar to those of figs. 108 and 109, obtained from the inner surface of the dura 



mater of a fetal pig of 90 mm. Enlargement, 285 diameters. 

 FIG. 111. Drawing of a preparation from the inner surface of the dura mater of a fetal pig of 16 cm. The specimen 



was made in the same manner as outlined in fig. 108. Enlargement, 285 diameters. 

 FIG. 112. Photomicrograph of a sagittal section of a pig embryo of 17 mm. An injection of an 0.5 per cent solution of 



nitrate of silver was made into the central canal of the spinal cord; the silver was reduced in sunlight 



and the embryo fixed in formalin. Enlargement, 13 diameters. 



FIG. 113. Photomicrograph, under higher powers, of the blocked areas in fig. 112. The accumulation of the reduced 



silver (psn) against the area membranacea superior is represented in black. Enlargement, 117 diameters. 



FIG. 114. Photomicrograph of a transverse section of a pig embryo of 19 mm. An injection of 0.5 per cent solution of 



silver nitrate was made into the central canal of this embryo and the silver immediately reduced in 



sunlight. The embryo was fixed in formalin, carefully dehydrated, and embedded in xylol-paraffin. 



Enlargement, 10 diameters. 

 FIG. 115. Photomicrograph, under higher magnification, of the blocked area in fig. 114. The collection of reduced 



silver (psn) against the cells at the inferior end of the area membranacea superior is illustrated. Enlarge- 

 ment, 100 diameters. 

 FIG. 116. Photomicrograph of a tranverse section of a pig embryo of 16 mm. The central canal of the spinal cord of 



this embryo was injected with a 1 per cent ferrocyanide and citrate solution under mild syringe-pressure; 



the embryo was then fixed in 10 per cent formol containing 1 per cent hydrochloric acid. Enlargement, 



10 diameters. 

 FIG. 117. Photomicrograph of the blocked area in fig. 116, under higher magnification. The accumulation of the 



precipitated injection fluid against the area membranacea superior is represented in black. A slight 



extraventricular spread of the fluid, which is found in this as in all embryos of this stage, can not be 



made out in the reproduction. Enlargement, 67 diameters. 



