The trachea of anthropoids generally includes from sixteen to eighteen cartilaginous rings, but in the siamang there are twenty-one. They ramify into branches which are, as a rule, wider on the right than on the left side.[79] There is a further lateral ramification on the right side, situated above the artery. Huxley and Ehlers hold that the lungs of a gorilla are cleft like those of the human organism, the right divided into three, and the left into two lobes. I have myself observed this type, and in one instance I found three lobes on the left. In the chimpanzee I saw that the right lung was divided into three, and the left into two lobes. Bischoff observed an instance of a chimpanzee which had four lobes on the right and two on the left side. In an orang dissected by me I found only one lobe on each side, with thin, slightly indented notches on the anterior edges of the right lobe, and two on the left, and there was at the same time a strongly marked indentation between the lobes. The lungs of a gibbon are described as having four lobes on the right, and only one or two on the left. I myself have examined a gibbon in which there were three lobes on the right, and two on the left. It appears that there are not unimportant individual variations of this structure in every species of anthropoids; and indeed, human lungs are by no means exempt from them. The male sexual organs correspond on the whole with the form and arrangement of these organs in man. I must not omit to mention that the penis of the swine-snouted baboon, and of other dog-headed apes, is much more like the penis in man than is the case with anthropoids, with the exception of the gorilla. In the last-named animal the scrotum is short and tightly stretched. The right testicle is a little higher than the left, and is divided from it by a wide raphé. The internal female organs are also like those of the human organism, with only slight variations. Bischoff is correct in the assertion that the external lips of the pudendum and the mons veneris are almost wholly absent. Bolau, Ehlers, and Hermes have ascertained that there is a menstruation which occurs periodically, at any rate in the case of the chimpanzee, and the other species cannot be exempt from the process. At such times there is a blush and enlargement of the external parts, and a profusion of the external lips of the pudendum, which are at other times scarcely apparent. The nymphæ and the clitoris are of considerable size and importance. There is often an excessive enlargement and reddening of these parts, as well as of the posterior callosities in the chimpanzee, and also in the baboon and macaca, during the period of sexual excitement. [Illustration: Fig. 56.--The brain of an orang, seen from the side (Vogt, from Gratiolet). F, Frontal lobe. P, Parietal lobe. O, Occipital lobe. R, Fissure of Rolando. S, Fissure of Sylvius. C, Cerebellum. ]