The ultrastructure of the ciliary muscle of an old crab-eating monkey, with special reference to specific inclusions.

The ultrastructure of ciliary muscle was studied in an old, healthy crabeating monkey. In the cytoplasm, large swollen mitochondria, interdigitated mitochondria, various types of myelin-like figures, dense coarse membranous structures, lysosomal dense bodies, round lipid-like bodies, transitional forms from lysosomal dense bodies to lipid-like bodies, lipofuscin pigments, whorl-like structures of agranular endoplasmic reticulum, coated vesicles, and multivesicular bodies were occasionally observed. Nexus was demonstrated between adjacent muscle cells. In the ciliary muscle, such findings were not only unknown in the earlier studies on the monkey species, but also some were never reported in any other species. Most of these inclusions were thought to be associated with cellular aging in relation to the presence of lipofuscin pigments and their related bodies, while the whorl-like structures might indicate either another type characteristic of the aged ciliary muscle or unknown pathological degeneration of the muscle. In addition, the possible occurence or the cytological significance of these inclusions, especially lipofuscin pigments, lipid-like bodies, whorl-like structures, dense coarse membranous structures, and myelin-like figures in the ciliary muscle, were discussed.