Bischoff has described the muscles which Halford terms _Contrahentes digitorum_ (contractors of the digits), which lie deep in the palm of the hands and feet of the chimpanzee and gibbon, the mandril, baboon, and other apes.[73] They rest upon the inter-osseous muscles, and are covered by the tendons of the long flexors of the digits, as well as by the lumbricales muscles. I have been unable to trace these _Musculi contrahentes_ in the gorilla. In a female chimpanzee I observed a _Musculus contrahens_ for the fourth, and another for the fifth finger, and the same for the fourth and fifth toes. In the orang I observed a _Musculus contrahens_ for the fourth, and one for the fifth fingers, and two faintly indicated _Contrahentes_ for the fourth and fifth toes. Similar muscles of the second, fourth, and fifth fingers, and of the fourth and fifth toes, may be observed in the white-handed gibbon. In correspondence with the height of the pelvic bones, the gluteus maximus of these animals only displays a moderate width in comparison with its length. The tendon which attaches it to the femur extends low down, almost as far as the knee-joint. The gluteus medius and minimus are also long, in correspondence with this structure of the pelvis, although they are attached to the large trochanter, and to the posterior inter-trochanteric line. The climbing muscle (_Musculus scansorius_), which extends between the hip-bone and the condyles of the femur, was discovered by Troill in the chimpanzee, and by Bischoff in the orang, and is described by them as strongly made; it appears to be absent in the gorilla and the gibbon. The pyriformis generally forms portions of the neighbouring muscles. The tensor vaginæ femoris, which is strong and wide in most anthropoids, is either greatly reduced or altogether absent in the orang. The sartorius is not, as in man, attached to the inner surface of the tibia, just below the internal tuberosity, but it is inserted much lower down on this surface. In the gorilla it has a tricipital attachment, one to the deep fascia of the thigh, and two others to the internal border of the tibia. In the chimpanzee and the gibbon the muscle extends equally low down. In the orang it does not go so far, but the _gracilis_ and _semi-tendinosus_ are in the same relative position. The biceps of the femur is very apparent in the orang; its long head divides in two parts, of which the lower is inserted in the fibula, and is here united with the short head.