ANATOMY OF MEGAPTERA LONGIMANA. 77 



enters the bone directly from the haemal groove, and its upper 

 opening is at first high on the side of the bone ; then, after the 

 complete neural arch ceases (on the llth), on what may be 

 termed the upper aspect of the bone ; but it is not till the 14th 

 or 15th, with the change to the square form of the body, that 

 the opening is fairly on the top. On the eight posterior vertebrae 

 (14th and backwards) it is simply a large, nearly vertical, rounded 

 canal on each side of the flat-sided bodies, through which one 

 may see, and is essentially the same on the three preceding 

 (llth, 12th, and 13th) vertebrae, but their widening body gives 

 the passage a curve outwards. These eleven posterior are the 

 vertebrae behind the chevron bones, and those which want a 

 complete neural canal. The lower aperture of the passage is 

 larger than the upper. The latter apertures are wider apart 

 than the lower. The following are the distances between the 

 upper apertures, in inches : On 18th caudal, 1 inch apart ; 

 14th, If ; 12th, 3 ; llth, 3J ; 10th, 3 J ; 8th, 4J ; 7th, 7J ; on 

 (itli caudal, 7| inches apart. 



The upper stage is present from the 7th back to the 14th. 

 On the first four (7th to 10th), piercing to a completed neural 

 canal ; on the second four (llth to 14th), piercing below the 

 low broad ridge which represents a commencing pedicle, to 

 reach the groove or pit which represents the floor of a neural 

 canal. (It is a groove and pit on the llth, a mere pit on the 

 12th, 13th, and 14th.) On the second four, the neural per- 

 foration does not, as on the first four, open separately on the 

 exterior, but goes in as a narrow passage from the middle stage 

 near the wide upper aperture of the latter. The perforation 

 representing the upper stage is either on one side only, or is 

 not symmetrical. It occurs only on the right side in the 7th, 

 9th, and 12th ; only on the left side in the 8th, 10th and llth, 

 13th and 14th, The 7th shows on the left side a groove in the 

 deep notch behind the pedicle, ascending from the second 

 stage of the passage, but not so far forward as the perforation 

 on the right side. On the 6th, the perforation has ceased on 

 both sides, but the notches are not symmetrical, the right 

 being more anterior than the left. Behind the 7th, the per- 

 foration is at the middle of the broad neural arch, and on the 

 side on which there is no perforation there is no notch or 



G 



