OEGANOGRAPHY. 49 



Free veins are 



Simple when each vein proceeds from the costa to the margin 

 without branching (83). 



Forked when they divide at an acute angle into two or more 

 branches after leaving the costa (51). 



Simply forked, or dichotomous, when the division is into two 

 branches (96). 



Pinnately forked when the primary veins are scarcely defined, and 

 branch several times one after the other on both sides (75). 



Pinnate when the primary veins that run from the costa to the 

 margin are distinctly defined, and produce venules in 

 regular order on both sides, so that the fascicles have a 

 feather-like appearance (121). 



Radiate when the veins spread out from a definite point at the 

 base of the frond or segment (93). 



The simplest form of anastomosing venation is when the apices 

 of the veins are combined or connected by means of a marginal 

 vein (113). In the more complicated forms it is spoken of as 



Angularly anastomosing when the venules of one vein join those of 

 the next, and form an angle at their point of junction (65) ; 

 when the angle is very acute the term acutely anastomosing 

 is employed, or sometimes called cathedrate. 



Arcuately anastomosing when the venules of one vein join those of 

 the next, and together form an arch or curve (63). 



Transversely anastomosing when the venules of one vein join those 

 of the next, and together form a nearly straight line (104). 



Distantly anastomosing when the venules are parallel with the 

 costa, close together, and joined at long intervals by short 

 cross veinlets. 



Compoundly anastomosing when the venules are irregularly con- 

 nected in a more or less net-like manner, and have variously 

 directed free or conniving veinlets in the areoles (21-28,43). 



Reticulated when the veins, venules, and veinlets are all connected 

 together in a more or less net-like manner : uniform is used 

 in reference to reticulated venation when there is no apparent 

 difference between the veins, venules, and veinlets (31, 55). 



