CHAPTER ONE 
EXTERNAL ANATOMY, REPRODUCTION AND DISTRIBUTION 
The European hamster, Cricetus cricetus Linee, 
belongs to the family Cricetidae and the subfamily 
Cricetinae of the order Rodentia. 
1.1 EXTERNAL FEATURES 
When kept under laboratory conditions, adult 
male European hamsters have an average body 
weight of 451 ± 49 g in summer and 245 ± 92 g in 
winter; while the adult females weigh an average 
of 359 ± 63 g in summer and 174 ± 49 g in winter. 
Under cold laboratory conditions (4°C; 90% rela- 
tive humidity) hibernating males and females have 
average body weights of 245 ± 92 g and 174 ± 49 
g, respectively (Reznik, et ai, 1973); the weight 
loss during winter is dependent upon hibernation 
(Fig. 0-2). Adult males have a mean length of 241 
± 9 mm and adult females of 237 ± 12 mm (Figs. 
1-1, 1-2; Table 1). 
The full-grown body is stocky, has a short tail 
('A of body length, or 3-6 cm) and the fur of the 
dorsal and lateral surfaces is yellow reddish-brown 
to grayish-brown in color (Figs. 1-1, 1-2). The tip 
of the snout, lips, throat and feet are white to 
yellowish-white, while the ventral surface is black 
(Fig. 1-1). Throughout summer, the dorsal surface 
is lighter in color than during winter (Kourist, 
1957). The hairs (pili) of the tail and the scrotum 
are much shorter than those on the rest of the body 
(Figs. 1-1, 1-2). During late summer and autumn, 
the animals have large subcutaneous fat deposits in 
preparation for hibernation (Fig. 1-3). 
On the head of the living European hamster, the 
black, round protruding eyes (oculi) are striking 
characteristics (Figs. 1-4, 1-5). Their deep black 
color is the result of very marked pigmentation, 
especially of the iris. A prominent planum nasale 
is formed by the epidermis. The nostrils (nares) are 
more broad than long and run obliquely caudally. 
A philtrum, which begins at the upper lip and ex- 
tends dorsally, is located in the mid-line between 
the two nostrils (Fig. 1-4, 2-9). No hair follicles 
can be seen around the nares; this portion of the 
planum nasale has a whitish-gray color. 
The facial whiskers or vibrissae are especially 
noticeable laterally on the upper lip of both male 
and female European hamsters. They are straight 
stiff hairs mainly occurring in two main colors, 
white and brown. They appear in four or five dis- 
tinct rows and consist of up to 30 hairs on each side 
(Figs. 1-4, 1-5). The length of the dark hairs is 32 
to 39 mm with root lengths of 0.585-0.730 mm. 
The maximal width is 0.166-0.191 mm above the 
root, narrowing towards the apex, which has a 
width of 0.005 mm. The measurements for the 
lighter-colored hairs are the following: length 7.5- 
25.1 mm, breadth 0.074-0.136 mm, root length, 
0.292-0.542 mm (Kourist, 1957). 
The prominent external ears, {auris externa), 
2.3-3.2 cm long in the adult (Figs. 1-4, 1-5), are 
translucent and relatively avascular in bright light. 
They are directed dorsomedially and appear short- 
er than they actually are due to the long body hairs. 
The soles of the hands and feet {palma manus, 
planta) demonstrate no sex differences (Figs. 1-6, 
1-7). The soles of the forefeet have five pads {ton). 
The hindpaws are very long (3.0-4.0 cm), with six 
pads on each paw. The arrangement of the pads is 
less symmetrical than that of the forefeet (Fig. 1-7). 
The pads vary in size on the hindfeet and the fore- 
feet, with the size increasing from the digits to the 
metapoidal joint in the forefeet, and decreasing in 
the hindfeet. 
When hibernating, it is difficult to distinguish 
the sex of the animals, as the testes lie intrapelvic- 
ally during this period of sexual inactivity. This 
does not occur in laboratory bred animals when 
kept under standard laboratory conditions through- 
out the year. 
Other characteristics which differentiate the 
sexes are the round preputial opening {ostium prae- 
putiale) and the space, about 2 cm. long, between 
the anus and prepuce {praeputium) in the male. 
(Figs. 1-8, 1-9, 1-10). In the female, the distance 
between the clitoris and anus is only about one cm. 
When the females are about 10 to 14 days old, eight 
teats {papillae mammae) (one cranial thoracic 
pair, one caudal thoracic pair, one abdominal pair, 
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