Of the _milk-teeth_, the incisors in the upper jaw change first. Of the molars, two are developed before the change of the pre-molars. In the lower jaw the incisors change first, and when two or three pre-molars have developed the last molar has still to come. The arm-bone, or _humerus_, has one perforation (_entepicondylar foramen_) on its inner margin, and another above the joint (except in _Perodicticus_). The bones of the fore-arm (_radius_ and _ulna_), and those of the leg (_tibia_ and _fibula_) are not co-ossified (except in _Tarsius_), so that the palm or sole can be turned up at will. The bones of the _digits_ are more or less flat and rounded at the tips (differing in this respect from the _Insectivora_). One of the ankle-bones, for the articulation of the opposable great toe, the ento-cuneiform, as it is called, is rounded, as in the Anthropoid Apes and Man. The thumb is opposable, but its articulating bone in the wrist is not rounded, except in _Avahis_ and _Indris_, which genera agree in this respect with _Anthropopithecus_ and Man. The wrist has its central bone (_os centrale_) present; it is absent in Man and the higher Apes. The knee is free and not united to the side of the body by integument. The two halves of the lower jaw are not always co-ossified (as is the case in the _Anthropoidea_). The opening in the base of the skull (the _foramen rotundum_) which transmits from the brain a branch of the fifth nerve {12}for the upper jaw, and the sphenoidal fissure, which gives exit to the third, fourth and sixth cranial nerves, have but one aperture, as in the Rabbit, which belongs to the _Rodentia_. The sacral vertebræ are generally three in number, and the lumbar and dorsal together vary from nineteen to twenty-three. The brain, as Sir William Flower has observed, departs considerably from the form of what may be called the primatial type, and approaches in form to that of the carnivorous animals. The hind-brain, or _cerebellum_, is not completely covered by the cerebrum. The latter has but few convolutions (indicating a low intelligence), but its posterior lobe is always present, though more or less rudimentary, and so also are many fissures, which are characteristic of its surface in the higher Primates. The olfactory lobes are usually large and not covered by the cerebrum. The uterus and structures for the nutrition of the young prior to birth are low in type, and approximate to the conditions seen in the Pig, the Horse, the Chevrotains, and the Ruminants. The unborn Lemur is often encased (as among the Sloths) in a skin-like covering (_epitrichium_) which breaks into patches before birth.