26 SCUDDER ON THE DEVONIAN 



The internomeclian vein seems to be represented by two widely separated simple veins, 

 the course of which, so far as they can be traced, would seem to indicate that they have a 

 common origin very near or at the base of the wing, directly below the common stem of 

 the scapular and externomedian veins. The upper In-anch first comes into view directly 

 beneath this stem, running parallel to it, and not very far away from it, but at double the 

 distance from it that the mediastinal vein is at this point, which is before the end of the 

 basal quarter of the wing ; when the mediastinal vein curves upward from the scapular, 

 this curves downward in about the same degree, until it reaches the distinct short cross 

 vein which unites it, as before stated, to the externomedian vein ; here it bends downward, 

 becomes more distinct than any of the nervules between it and the main scapular vein 

 (previously it had been rather inconspicuous), and runs in a nearly direct faintly arcuate 

 course to the middle of the lower margin of the wing, gently diverging throughout from 

 the externomedian vein and its nearer branches. The lower branch is first seen in the 

 . very centre of the basal third of the Aving, from which point it passes in a nearly straight 

 course almost parallel to the distincter portion of the other branch, and is as heavily 

 marked. The anal vein is perhaps simple, running at first downward and curving outward, 

 subparallel to but distant from the lower basal margin, becoming just before the middle of 

 its regular course straight and distinct, when it diverges slightly from the border of the wing, 

 and inclines distinctly although not greatly toward the lower internomedian branch, con- 

 tinuing in this course until it reaches a distinct oblique cross vein which unites it to the 

 latter in the middle of the basal half of the wing ; here it bends abruptly downward at 

 ricdit angles to the cross vein, and runs doubtless into the margin ; the cross vein is nearly 

 transverse to the interspace in which it lies, and is about parallel to, and is of the same 

 leno-th as, the upper limb of the bent cross vein in which the mediastinal vein terminates. 

 Next the basal margin of the wing is a brief simple shoot directed almost vertically 

 downward, which may be an inferior basal branch of the anal vein. The other lines 

 between the internomedian veins and the margin, seen in fig. 5, represent merely fractures 

 in the stone. 



Besides the three distinct cross veins mentioned, — (1) that in which the mediastinal 



vein terminates, (2) that between the upper internomedian branch and the externomedian 



vein; and (3) that connecting the lower internomedian branch and the anal vein — 



and the weak cross veins visible in the interspace above the mediastinal vein (of which 



only those in the basal half are represented in fig. 5), there are in various parts of 



the wing exceedingly indistinct, very weak, very closely approximated, but unequally 



distant cross veins, transverse or nearly transverse to the interspaces, sometimes 



curved but never showing any tendency to unite so as to form any kind of reticulation ; 



it is probable that they exist throughoiit the wing, or at least below the main scapular 



vein ; they are most distinct in the externomedian interspaces, and in those on either 



side of the internomedian branches, especially next the nervules themselves, as 



may be seen in fig. 5 on either side of the lower internomedian branch, where they 



are more distinct than in any other part of the wing ; this mode of fracturing the 



interspaces, rather than reticulation, is the more marked from the exceedingly open and 



distant neuration. 



