THE POSITION OF FIGURES. 31 



Hold a book and note its several aspects — the top and bottom, the hach 

 and front, the right and left sides. For the purpose of comparison, these 

 aspects may be considered to correspond with the head and caudal aspect, 

 the hack and the belly, the right and left sides of a man or a cat. 



When the book is held so as to permit the reading of a title printed 

 across the back, the various aspects coincide in position and direction with 

 the body-aspects. The right is at the right of the observer, and the left at 

 his left ; the back faces in the same direction with his own, v/hile the top of 

 the book is upward, and its bottom down. 



But when the book is held just ready to be opened, the top and bottom 

 have the same directions as before, but the back and front, the right and 

 left sides are reversed. The right of the book is opposite the left of the 

 observer, and vice versa. 



In the first case, the observer and the book are related as are two persons 

 one behind the other; in the second case, the relation is that of two persons 

 facing each other, and as when one views his own image in a mirror. 



Again, if the book is held^so that the loiver end is in view, the right and 

 left still correspond with those of the observer; but if it is turned so as to 

 expose the top, then the right and left are reversed. The same difPerence 

 exists in the case of transections of objects. If a book were cut across, there 

 would be exposed two cut surfaces, the bottom surface of the upper part, 

 and the top surface of the lower part. With an animal, these would be 

 called the caudal surface of the cephalic part, and the cephalic surface of 

 the caudal pai't. If the former is viev/ed, the right and left of the surface 

 coincide with those of the observer; if the latter, then the right and left are 

 reversed. 



As with objects, so with their representations in j^ictures and diagrams. 

 The right and the left, the dorsal and the ventral aspects, are to be so desig- 

 nated, whatever may be tlieir position on tlie page or ivitti respect to tlic 

 observer. 



The foregoing remarks concern symmetrical figures, which represent 

 either the dorsal, the ventral, the caudal or the cephalic aspects of an ani- 

 mal, or its parts. As a rule, in the j^resent work, such figures are so placed 

 that the meson coincides in direction with that of the observer, and with the 

 longer diameter of the page, as, e. g.. Fig. 2 and 3. 



Figures which, like Fig. 4, are ^msym metrical, and represent the lateral 

 aspects of animals or their parts, are usually so placed that the meson lies 

 across the page, and at a right angle with that of the observer. Usually, 

 also, in accordance with distinguished precedent, as remarked in a paper 

 (17) by the senior author, the cephalic end of such figures is turned toward 

 the left of the page and of the observer. 



§ 57. Position and Direction on the Soma.— The letters A, B, C, 

 D, E, F, G, H, I, K, with the dotted lines between them are introduced for 



