Functional anatomy and sexual dimorphism of the cephalic clasper in the pacific ratfish (Chimaera collei).

The cephalic clasper of the male Chimaera collei is a cartilaginous rod equipped with denticles and presumably used to grasp the female during copulation. It is attached to the skull by ligaments but there is no joint cavity or articular surface. It has no intrinsic muscles, its movements being provided by attachments to muscles of the lower jaw and labial cartilages. The cephalic clasper is apparently elevated by a branch of the preorbitalis muscle, whose main function is to elevate the lower jaw. It appears to be forcefully depressed during copulation by M. levator anguli oris, whose primary function is to move the labial cartilages. When not in use, the cephalic clasper is held passively depressed by an elastic tendon from M. preorbitalis. In the female the cephalic clasper is represented by an apparently functionless rudiment.