Ch. XI] 



SERIAL MICROSCOPIC SECTIONS 



409 



Sagittal Sections 



§ 664. Sagittal sections are those made parallel with the long axis 

 of the body and from the dorsal to the ventral surface, thus dividing 

 the object into equal or unequal right and left (dextral and sinistral) 

 parts. 



(1) Imbed the animal or embryo with the right side down in the 

 imbedding mass (§612); and arrange the object exactly over the 

 orientation diagram in the bottom of the imbedding box (§657). 



Sagittal 



Imbedded Embryo 



Fig. 242. Serial Sagittal Sections Showing the Position of the Embryo 

 in the Imbedding Mass, the Connection with the Microtome Holder and 

 the Arrangement of the Sections on the Glass Slide. 



Microtome Holder The metal disc and stem for holding the embryo in position 

 while it is being cut. 



Imbedded Embryo The imbedded embryo in the proper position for sagittal 

 Sections. 



Sagittal Sections A slide of sagittal sections in the proper position on the slide. 



1, 2 Serial order in which serial sections are arranged on the slide. 



In section 2, the word sinistral indicates that the left surface of the section faces 

 directly upward. The right side rests upon the glass. 



The words cephalic, caudal, dextral and sinistral are inverted under the com- 

 pound microscope, the sections are reinverted, and will appear like this picture, if 

 the book is turned upside down. 



(2) Mount the block of paraffin containing the embryo so that the 

 right side w T ill be next the disc of the microtome holder. The left side 

 will then be cut first, and look up when mounted (fig. 242). 



(3) Place in the microtome so that the caudal end will first meet the 

 edge of the knife. 



(4) Mount the sections in the order of the print on a page. This 

 will bring the caudal end to the left, the cephalic at the right, ventral 

 aspect up and dorsal down toward the lower edge of the slide. The 

 dextral face of the section will rest on the slide, and the sinistral face 

 will look up. 



