OF THE STURGEON. 
355 
of the carelessness with which this structure has been stu- 
died, that the only author who delineates it represents the 
membrane on both sides of the axis as reticular. This over- 
sight I have attempted to rectify, (Fig. 3.) 
The aor^is or central pillar of the valve seems to consist 
of bloodvessels, enclosed in cellular tissue, and enveloped 
in the same smooth uniform membrane which lines the 
sinuosities on its left side. The author to whom I last 
alluded, the late Dr Monro of this University, in his work 
on the Structure of Fishes, denominates the axis the 7ne- 
senteric veins; and the membranous slips proceeding from 
it to the intestines, hranches of these veins. This I cannot 
help regarding as a most fanciful and erroneous notion, 
which I can neither explain nor reconcile with the accuracy 
and zeal with which that able anatomist laboured to extend 
the bounds of our knowledge of the structure of the animal 
world. There is in the axis no appearance of venous 
trunks sufficiently large to constitute the mesenteric veins ; 
nor do the slips contain any vessel entitled to the epithet 
of branches of these veins. It is very probable that the 
Doctor never examined their interior structure, and upon 
some loose analogy, or imaginary resemblance, took it for 
granted that the axis and its spiral membrane was a vas- 
cular distribution. I examined it by means of longitudinal 
and obhque incisions, but could find neither to my own 
satisfaction nor to that of the gentlemen present, any vas- 
cular arrangement more than that of small vessels, sent, as 
might be expected, to supply the axis. I regret that the 
circumstances under which our dissection took place, ren- 
dered it impossible to inject any part of the animal ; but 
I shall avail myself of the earliest opportunity to supply 
this defect, and determine the point positively. 
The use of the spiral valve is sufficiently obvious. The 
intestinal tube is not, as in the Mammaha and Birds, 
z 2 
