Fig. 40.--Human skeleton.--_a_, Parietal bone. _b_, Frontal bone. _c_, Cervical vertebræ. _d_, Sternum. _e_, Lumbar vertebra. _f_, Ulna. _g_, Radius. _h_, Carpus. _i_, Metacarpus. _k_, Phalanges. _l_, Tibia. _m_, Fibula. _n_, Tarsus. _o_, Metatarsal bones. _p_, Phalanges. _q_, Patella. _r_, Femur. _s_, Os innominatum. _t_, Humerus. _u_, Clavicle. ] [Illustration: Fig. 41.--Skeleton of an aged male gorilla.] The excessive curvature of the forearm which we notice in the gorilla and the chimpanzee in their natural condition is rare in man, and when it does occur it must be regarded as an abnormal and pathological phenomenon. The orang-utan always displays a ninth carpal bone, corresponding to de Blainville’s _os intermedium_ and Gegenbaur’s _os centrale carpi_. In a very young animal I found that this small bone was furnished with a peculiar point of ossification. The bony structure of the wrist is developed in the following succession:--First, the _os magnum_ and unciform bones; second, the scaphoid bone; third, the trapezium; fourth, the semi-lunar bone; fifth, the cuneiform bone; sixth, _os centrale carpi_; seventh, the trapezoid bone. The pisiform bone and the sesamoid bone, between the trapezium and the scaphoid bone, of which we shall speak presently in their relation to the muscular system, are at first simply cartilaginous. Up to this time my search for this ninth carpal bone in the gorilla and the chimpanzee has been fruitless, since its occurrence is only exceptional. In the gibbon it is plainly inserted between the scaphoid, semi-lunar, trapezoid, and _os magnum_. Gegenbaur considers the _os centrale_ to be a true constituent of the wrist, dating from an earlier condition, but he has nothing to suggest as to its subsequent survival. Rosenberg has lately given an incontestable proof of the presence of this bone in the human embryo. It is generally absorbed again, but sometimes it persists, and may be found in an adult as a well-formed ninth carpal bone. Cases of the persistence of the _os centrale_ in man have been chiefly collected and published by the diligence of the Russian anatomist, Gruber. It is now suggested that there may also be indications of _os centrale_ in the carpus of embryos of the gorilla and chimpanzee, but up to this time materials for such researches have been wanting.