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3. Notes of the Dissection of a Female Beaver. By John 
Cleland, M.D., Demonstrator of Anatomy, University of 
Edinburgh. Communicated by Dr Douglas Maclagan.* 
In this paper the writer directed attention to the remarkably de- 
veloped parotid glands of the beaver, which form a single large mass 
covering the whole front and sides of the neck, and cannot be sepa- 
rated from one another. He showed how the apparent disproportion 
between the anterior and posterior extremities of the beaver was in- 
creased by the way in which the parietes of the abdomen overhung 
the thighs, and the margin of the panniculus carnosus passed over 
the knees so as to include them in the muscular investment that 
enveloped the trunk. 
The use of the horny development, called by zoologists an addi- 
tional nail, on the second toe of the hind foot, was explained thus : — - 
the toes, especially the first and second, are curved inwards for pur- 
poses connected with the animal’s aquatic habits ; and when it 
supports itself in its favourite posture on its hind legs and tail, these 
two toes lie with their outer sides downwards. The innermost is 
small, and bears none of the weight ; but the second toe bears a con- 
siderable amount, and the tender matrix of the nail would be con- 
stantly pressed against the ground, were it not that the horny 
development is so shaped that, while it presents its under surface to 
the earth, the superior aspect fits in to the concavity of the claw above. 
The dilatation of the vena cava for diving purposes was described, 
and the arrangement of the castor sacs. 
The principal points with regard to the latter are as follows : — - 
The rectum and genito-urinary aperture open into a common de- 
pression as in the male, and the oil glands and general form of the 
castor sacs resemble those of the male ; but while in the male the 
necks of the castor sacs of opposite sides are united by a communi- 
cation above the preputial opening — i. e ., between the prepuce and 
rectum — -in the female they are united by a dilatation like a small 
third lobe, situated, not on the superior aspect of the genito-urinary 
aperture as in the male, but on the pubic aspect ; and the clitoris 
appears on the anterior margin of the dilatation immediately inferior 
to the urethral orifice. The castor sacs and oil glands are invested 
by a muscular tunic, whose fibres, arising superiorly in connection 
* Published in full, with a plate, in the Edinburgh New Philosophical 
Journal, New Series, vol. xii. p. 14. 
