Henry L. Bruner Hs 
described the muscle as a homologue of the striated m. depressor palpe- 
bre inferioris of Weber, 77. The nature of the muscle explains the 
slow movements of the lower eyelid of the turtle; it also probably ac- 
counts for the very gradual reduction of the sinus orbitalis. Under 
ordinary conditions the muscle probably maintains a tonus which keeps 
the eyelids retracted and prevents distension of the sinus orbitalis. The 
elevation of the lower lid in Emys seems to be due chiefly to blood- 
pressure, as is the case in the lizard. In Emys there is no special muscle 
for the elevation of the lower eyelid, such as Stannius, 54, Vol. II, p. 172, 
has observed in Chelydra and Chelonia. 
C. SIGNIFICANCE OF THE SWELL MECHANISM IN THE HEAD 
OF TESTUDINATA. 
The experiments with Clemmys seem to show that the distension of 
the cephalic veins and sinuses has the same significance in the turtle as 
in the lizard. ‘They confirm the view which is naturally suggested by a 
study of structure, that the swell mechanism of the turtle is a true 
moulting mechanism. On the other hand, however, we are confronted 
by the fact that a typical moulting process does not occur in the Testu- 
dinata. According to Gegenbaur, 98, the stratum corneum of the turtle 
wears away gradually and is renewed in the same way from below. 
Under the circumstances, the retention of the moulting mechanism may, 
perhaps, be explained on the theory that the method of desquamation has 
not reached a state of perfection which renders the mechanism wholly 
superfluous in getting rid of the old stratum corneum. Until additional 
evidence shall prove the contrary, therefore, we may consider the swell 
mechanism of the turtle as a true moulting mechanism. 
IV. ONTOGENY OF THE BLOOD SINUSES OF THE 
REPTILIAN HEAD. 
The ontogeny of the blood sinuses of the reptilian head has been in- 
vestigated by Grosser and Brezina, 95, who find that the sinus orbitalis 
is formed by the gradual enlargement of a system of capillaries and veins, 
chiefly the vena orbitalis inferior and its tributaries, all of which are 
gradually distended until the soft tissues are largely displaced and a 
continuous sinus is formed which surrounds all the organs of the deeper 
part of the orbit. In an embryo of Lacerta agilis, series 20, head 6.3 mm. 
long, the adult condition has already been attained. 
The numerous smaller sinuses of the head, which represent all stages 
of enlargement from the dilated capillary to the sinus palatinus, have, 
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