OF THE ORNITHORHYNCHUS PARADOXUS. 
525 
veys the urine and the genital products into the second or external cavity : for 
this part he retains the name, originally given to it by Sir Everard Home, 
of vestibule, as it affords a common outlet to the preceding substances and the 
contents of the rectum. 
The common vestibule is about one inch four lines in length, and varies 
from half an inch to an inch in diameter. The muscular fibres immediately 
investing it are disposed as follows. A thin circular muscle arises from a 
dorsal raphe which extends the whole length of the canal. Of this muscle the 
sacral fibres, or those nearest the outlet, surround the whole vestibule ; but 
the atlantal or more internal fibres pass obliquely upwards and surround the 
termination of the rectum only, serving as a sphincter to it. On the sternal 
aspect of the vestibule there are a series of longitudinal fibres, which ex- 
tend from its external orifice to that of the urethro-sexual cavity, the office 
of which is to approximate these orifices, and in this action the oblique 
fibres above described would assist, while at the same time they closed the 
rectum. 
On the sternal aspect of the urethro-sexual cavity, and close to where it 
joins the vestibule, the clitoris is situated, which is consequently about an inch 
and a half distant from the external orifice of the vestibule. It is inclosed in a 
sheath upwards of an inch in length, and about two lines in diameter, of a 
white fibrous texture, and with a smooth internal surface, and this sheath corn- 
municates with the vestibule about a line from the external aperture. The cli- 
toris itself is a little flattened body shaped like a heart on playing-cards ; it is 
about three lines long, and two lines in diameter at its dilated extremity, where 
the mesial notch indicates the correspondence with the bifurcated penis of the 
male. From the shortness of the clitoris, and the length of its sheath, it is ob- 
vious that no part of it can project into the vestibule in the ordinary state of the 
parts, as stated by Sir Everard Home, its extremity being situated at least an 
inch distant from where its sheath communicates with that cavity. At the base 
of the clitoris are two small round flattened glands which open into the sheath 
or preputium clitoridis. These glands were largest in the specimen whose ute- 
rine organs were most developed. The vestibule is lined by a dark-coloured cu- 
ticular membrane, and has a tolerably uniform surface. The rectum opens freely 
into it posteriorly, the line of distinction in the relaxed state of the sphincter 
3 Y 
MDCCCXXXII. 
