Unusual blood vessels in the cochlea of the squirrel monkey.

Unusual blood vessels in the cochlea of the squirrel monkey are reported. The blood vessels in Reissner's membrane and basilar membrane are occasionally found in the course of the experimental middle ear study. The blood vessel of Reissner's membrane derives from a radiating arteriole in the upper spiral ligament and takes a straight course down to the inner surface of the spiral limbus, running on the scala vestibuli side of Reissner's membrane, and finally joins the venous vessel of the spiral limbus. Two blood vessels are noted in the basilar membrane of basal turn, running fairly parallel to each other from the tympanic lip to the basilar crest of the spiral ligament in the same cochlea. It is confirmed that these unusual blood vessels derive from the radiating arterioles in the osseous spiral lamina and connect with the venules of the basilar crest in the spiral ligament. Although unusual blood vessels in both Reissner's membrane and basilar membrane are thought to be vestigial structures, they contain a remarkable amount of alkaline phosphatase in their walls. This suggests that these unusual vessels have actually functioned until their death. Multiple occurrence of unusual blood vessels in both Reissner's membrane and basilar membrane of the cochlea of various animals, including man, has not yet been reported in the literature as far as we have been able to ascertain. Incomplete devascularization in the developing process of the cochlea may possibly be the cause of such unusual conditions after birth.