18 
DE. H. GADOW OX THE CLOACA AND ON THE 
by two very large triangular flaps, one on each side, which arise from the inner, or 
median, root of each penis, and extend towards the medio-ventral line to the ventral 
or anterior margin of the anus. Each flap, more or less horizontally, lies inside the 
anal sphincter, so that, if the latter is closed, it is hidden from view. In the verti- 
bulum thus formed open the penes and the neighbouring anal glands. 
The slit between the free margins of the two flaps leads into a somewhat larger 
chamber, which is shut off from the rectum by a strong more or less circular fold. 
This fold is, however, very low on the ventral, but very high and thick on the dorsal 
wall. Thus is formed a rather deep dorsal recessus, into which open the urino-genital 
canals. In Monitor, Lacerta, Anguis, Calotes, the ureter and the vas deferens of each 
side are united into one short canal, which opens on a small papilla ; in the female 
the two oviducts and the two ureters have four separate openings. In the genus 
Lophura both ureters unite, form a small pseudo-bladderlike dilatation, and open on 
one papilla in the dorso-median line ; the oviducts have likewise one outer opening 
only, situated a little nearer towards the pelvis than the urinary opening, but they 
are divided by a longitudinal septum, which extends almost to their orifice. 
The urino-genital recessus is surrounded by a thick and low nearly circular fold, 
formed entirely by the dorsal wall ; it can close the recessus almost completely. This 
fold is arranged in such a way that, when pressed upon by the faeces coming from the 
rectum, the recessus is completely protected, but otherwise it leads the urine towards 
the urinary bladder, or, if that organ be not developed, into the rectal chamber. 
This rectal chamber is very capacious and is marked off both against the rest of 
the rectum and against the cloaca by high and strong semicircular folds. Its internal 
structure in L. ocellata and L. viridis agrees with that of the rest of the rectum (which 
can sometimes form another pouch-like dilatation), but in Monitor its quite smooth and 
thin walls, with a very feebly-developed layer of circular muscle-fibres, bear more 
resemblance to the cloaca than to the rectum. 
Most Lizards, with the exception of the Monitors, Amphisboenidce, and some 
Agamidce, possess a true urinary bladder ; it is often of considerable size, and opens 
by a narrow tube on the ventral side exactly on (or slightly analwards from) the fold 
between the lower rectal and the urino-genital chamber. This position explains how, 
if the anal opening be firmly closed and the whole vestibulum be compressed, the urine 
can enter this bladder ; and, secondly, how, by contraction of the bladder, part of the 
urine can enter the rectal chamber and there mix with the fasces, which, as is well 
known, almost invariably contain portions of the whitish-yellow urea. This rectal 
pouch is, therefore, a true cloaca in the physiological sense. 
In the Monitors the inner divisions between the vestibulum and the urino-genital 
chamber are not well marked, and it is only by artificial means that folds corre¬ 
sponding to those of the Lacerta can be traced. 
The Ophidian type (fig. 19) is similar to that of the Saurians. The rectum forms 
a capacious, thin-walled, and smooth chamber, which can be shut against the rest of 
