CI I. VII.] SERIAL SECTIONS. 169 



tions or longisections can be made. Organs like the liver and other 

 glands, the skin, etc., should be so arranged that sections parallel with 

 the surface or at right angles to it, (surface or vertical sections) may be 

 made. Oblique sections are often very puzzling. 



With cylindrical objects, especially botanical specimens, one may cut 

 tangential sections, i. e., sections at right angles to a radius, or parallel 

 with the radii (radial sections), or transections, i. e., sections across 

 the long axis. 



§ 2S7. Arrangement of Serial* Sections. — The numerical order 

 may be very conveniently like the words on a printed page, from the 

 upper left hand corner and extending from left to right, top to bottom 

 (Fig. 135). 



The position of the various aspects of the sections should be in gen- 

 eral such that when they are under the compound microscope the rights 

 and lefts will correspond with those of the observer. This may be ac- 

 complished as follows for sections made in the three cardinal sectional 

 planes, Transections , Frontal Sections, Sagittal Sections : 



(A) Transections, i. e., sections across the long axis of the embryo 

 or animal dividing it into equal or unequal cephalic and caudal parts. 



(a) In accordance with the generally approved method of numbering 

 serial parts in anatomy, the most cephalic section should be first (No. 

 i of Fig. 135). 



(b) The caudal aspect of the section should face upward toward the 

 cover-glass, the cephalic aspect being next the slide. 



(c) The ventral aspect should face toward the upper edge of the 

 slide (Fig. 135). 



This arrangement may be easily accomplished in transections in two 

 ways : (1) The embryo or animal is imbedded in such a way that the 

 sectioning shall begin at the cephalic end. In this case the first section 

 is placed in the upper left hand corner of the slide (No. 1 of Fig. 135), 

 but it must be turned over so that the caudal aspect shall face up. 

 The ventral aspect must be made to look toward the upper edge of the 

 slide, then under the compound microscope the dorsal side will appear 

 toward the upper edge of the slide and the right and left correspond 

 with the observer. 



(2) The embryo or animal is imbedded so that the sectioning begins 

 at the caudal end, then the sections are not turned over, as they are al- 

 ready caudal face up, but the}' must be put on the slide in reverse order, 

 i. e., the first section made is put in the lower right hand corner (No. 

 10 of Fig. 135). In this way the most cephalic section will be number 

 one as before. As in the previous case the ventral side of the section 

 should be toward the upper edge of the slide (Fig. 135). 



