The Mechanics of Respiration in Turtles

here presented it would seem unlikely that any true homology exists between the supranasal sac of the Viperinae and the facial pit of the Crotalinae. The two differ markedly in their morphology and anatomical relations as well as in innervation. It is not surprising that both are innervated by the trigeminal since this nerve furnishes the chief supply for sensory endings of the whole surface of the head. That there is some concentration of nerve endings in this region is not to be denied but it is extremely slight as compared with that in the region of the facial pit of the pit-vipers or even as compared with the concentration of nerve endings in the labial pits of the pythons and boas. The conclusion seems justified that in these three groups of snakes, the Crotalinae, the Viperinae and the Boidae we have three separately evolved types of sense organs all possessing trigeminal innervation.