dextrad, sinistrad, ventrad, and dorsad. Thus a part which 

 extends in a cephalic direction may be said to extend cepha- 

 lad. 



Lateral and laterad — The terms dextral, dextrad, 

 sinistral, and sinistrad, are seldom used in the following 

 pages, as it is rarely necessary to specify one side as dis- 

 tinguished from the other. Instead of these terms lateral 

 and laterad are used. 



Bxamplr. — The wings are lateral appendages of the body ; and in 

 most dragon-flies they extend laterad when the insect is at rest. 



It is important here to define more definitely the direc- 

 tions indicated by these six sets of terms. 



When we say that a certain part extends dextrad, we do 

 not mean necessarily that it extends towards the right side 

 of the animal or even towards a plane tangent to the right 

 side of the animal ; but that it extends towards a point which 

 is in a certain well understood direction* and which is at an 

 infinite distaiice in that direction. We are thus able to indi- 

 cate the position of an object which may be far exterior to 

 the body of the animal with whose position we are compar- 

 ing it. This is perfectly in accordance with the popular use 

 of the terms right and left. 



According to this definition, all lines extending right and 

 left across the body of an animal are parallel. 



The same may be said respecting ventro-dorsal lines. 

 Dorsad being eqdivalent to behind in the sense in which it is 

 applied to the body of man, or above as applied to the body 

 of a quadruped when in its natural attitude. 



// is also true that all caudo-ccphalic lines are parallel. 

 This is a point to which careful attention must be paid, else 

 there is liability to error. It is quite natural to think that 

 cephalad means towards the head or towards the head end of 

 the body axis, and that caudad means toward the tail. The 

 fact is that cephalad means towards a point which is in a di- 



* Indicated by a line drawn at right-angles to the cephalo-candal and dorsoven- 

 tral axes and towards the right side. 



