Introduction 
In our experience the squirrel monkey {Saimiri sciureus, Voigt, 
1831 ) has proved to be an excellent experimental animal for many kinds 
of brain and behavioral work for which a primate form is desired (1,4, 
5, 6) . Unlike the larger primates, this New World monkey has the ad- 
vantage that its brain, which is comparable to the cat’s in weight and 
size, is of desirable dimensions for combined neurophysiological and 
neuroanatomical investigations. There is the added advantage that its 
small body makes it easy to handle and economical to maintain. Rep- 
resentative measurements of its body and brain are given in table I. Some 
details in regard to the purchase and maintenance of the squirrel monkey 
are discussed in the appendix. 
Table I— REPRESENTATIVE BODY AND BRAIN MEASUREMENTS OF 
THE SQUIRREL MONKEY* 
Weight 
Body length . 
Tail length . . 
Total length. 
Head length. 
Head width . 
Brain weight 
Brain length. 
Brain width . 
Number 
of 
animals 
Mean 
Standard 
deviation 
76 
717 g 
±170. 4 
49 
260 mm 
±24. 7 
50 
360 mm 
±21. 4 
48 
630 mm 
±35. 7 
45 
54 mm 
±2. 2 
45 
41 mm 
±3. 6 
21 
26 g 
±1.7 
29 
49 mm 
±2. 1 
30 
35 mm 
±1. 7 
* (From: Carmichael, M. and MacLean, P. D. EEC Clin. Neurophysiol., 1961, 13: 128-129.) 
The squirrel monkey is indigenous of Central America and of ex- 
tensive areas of northern South America. It belongs to the family 
Cebidae. The generic term Saimiri (which is assigned a masculine 
gender) is presumably an Indian term for this particular type of mon- 
key.^ Hill ( 2 ) gives an extensive taxonomical description of a number 
of species and subspecies, as well as some information about their terri- 
torial origin and general behavior. The Saimiri are arboreal animals 
characterized by an elongated oval head, a somewhat flat face with 
closely placed eyes, and a long, nonprehensile tail. The common squirrel 
monkey (Saimiri sciureus) has soft, orange-brown to grey colored fur 
which is of similar hue on the back and crown. 
In answer to requests for stereotaxic data on the squirrel monkey, 
we have sent to several laboratories a duplicated line drawing atlas. 
Continuing requests for this material have encouraged us to proceed 
with a publication of the present photographic atlas. 
^ Personal communication from Dr. David H. Johnson, Curator of Mammals, United States 
National Museum. 
1 
