16 
DR. H. GADOW ON THE CLOACA AND ON THE 
Saurians and Birds, but in neither case would the folds bordering its cephalic and 
caudal ends correspond with those of the other Sauropida. In fact the urinary 
compartment described above is homologous with the chambers UD and CD of the 
Saurians, Snakes, and Birds. This I am able to prove by the condition of things 
prevailing in very young, but already hatched, Crocodilia (fig. 23). In Alligator 
mississipiensis (snout to anus 13 cms.) the ureters open into a small roundish chamber, 
which is bordered head- and tailwards by a high and very prominent circular fold. 
The fold towards the head is situated closely above the urinary orifices, and leads into 
a slightly larger chamber, CD, the inner walls of which are very irregular through 
high longitudinal and oblique folds; the lumen of this chamber CD is small, and 
shows the same internal structure as the rectum above, from which it is separated by 
another prominent and very thick fold. Externally both chambers CD and UD are 
surrounded by a powerful layer of chiefly circular muscles, which mark the termina¬ 
tion of the rectum very distinctly, and give the chambers UD and CD the external 
appearance of one swollen bulb. The inside of both chambers shows numerous folds, 
finer and more villous in UD. In young Crocodilus palustris (snout to anus 11 cms.) 
a very similar condition prevailed, but the inside of chamber UD w r as smooth, velvet¬ 
like, and remarkably different from that of CD, the mucosa of which showed the same 
structure as the upper rectum. In young Crocodilus biporcatus (snout to anus 15 cms.) 
a remarkable difference is observed. The fold rc has almost entirely disappeared, 
and the chamber CD, besides now forming one compartment with UD, is consider¬ 
ably elongated ; the inside shows only a few longitudinal folds, the walls of the two 
united chambers are thin, and much of the former strong muscular coating has given 
way to thin longitudinal fibres. 
In still older specimens of Crocodilus and Alligator the original two chambers are 
transformed into one thin-walled, much-distended, and inside almost smooth compart¬ 
ment, shut off from the rest of the rectum by a sphincter and fold like that of the 
adult. This shows that the peculiar arrangement of the adult Crocodilia is secondarily 
acquired, and that part of the rectum, viz., CD, is transformed together with UD 
into a room intended for the exclusive retention of urine. The outer, posterior or extra- 
pelvic chamber (vestibulum) is characterised by a much stronger development of the 
longitudinal muscles, a considerable portion of which goes as a detached band to the 
post-anal region of the tail (cf p. 14); its dorsal wall is much longer than the ventral, 
like in all animals with a longitudinal anal opening. Near its lateral margin opens on 
each side a complicated musk-gland at the fundus of a deep recessus. The walls of 
the latter can, like those of the gular musk-glands, be everted at will like the finger 
of a glove, chiefly through the pressure of the superimposed M. sphincter transversus. 
The smeary contents of the gland-bags are pressed out by the non-striped muscular 
coating of the bags, from which runs a likewise non-striped cord to the crura penis. 
It is generally supposed that through these strong scent-glands the sexes are enabled 
to find each other, but besides this sexual advantage they seem to be used as warning 
