The cynomolgus monkey as a model for orbital research. I. Normal anatomy.

Significant differences in anatomy preclude the use of the more common small research animals in orbital studies. One must look to the anthropoid apes to find a species comparable to man in both bony skeleton and soft tissue contents. While the orbit of the cynomolgus monkey is remarkably similar to that of man, differences still do exist. In this monkey, the ethmoid, frontal and sphenoid sinuses are absent, and the os planum of the ethmoid is represented in only a minority of younger animals. A technique for microscopic examination of the soft tissue contents of the orbit has likewise shown a basic similarity to man, with minor, yet possibly significant, differences in extraocular muscles, connective tissue septae and the lacrimal gland. A recognition of these similarities and differences allows utilization of this animal as a useful model in orbital research.