Body Organs

The Hand contains a total of 27 bones and is the most flexible part of the human skeleton. Like other higher primates, humans possess nails instead of claws and have a thumb that can be rotated to oppose the other digits, enabling them to manipulate objects delicately and precisely. Higher primates other than humans, however, also use hands for locomotion; the development of an upright posture and consequent use of the hands for manipulation alone probably took place concurrently with the increase in brain size in humans. Shown here are some of the major muscle and tendon systems for moving the bones of the thumb and other digits. The human foot differs from the feet of other higher primates in that it is used solely for locomotion, so that the big toe is no longer opposable to the other digits as it is in the great apes. Instead the bones of the feet have evolved in a way that enables humans to stride, and toes other than the big toe begin to show signs of degeneration. The heel bo

Male and female human reproductive system develop from a similar set of embryological structures and many structural and functional parallels exist. Individual difference occur in the shape and structure of genitals, but without interfering with reproductive or sexual function. Also, the sexual anatomy of a young child differs from that of a mature adult, and in turn, adult sexual anatomy alters in the later years of life. Male Reproductive System The male reproductive system basically is designed to produce and transport sperm cells. At the same time, the male genitals play an obvious role in sexual behavior, because reproduction cannot take place unless sperm cells are deposited in the female reproductive system. The major organs of the male reproductive system are the testes (testicles), the prostate, the seminal vesicles, the vast deference, the epidermis, and the penis. Testes The testes, which are contained in a pouch of skin called the scrotum, are located outside of the