Rickets in children is caused by the deficiency of which vitamin?

The correct answer is D, the sartorius. It is a thin, strap-like muscle that runs across the front of the thigh from the hip bone to the inner side of the knee, and because it crosses two joints it is the longest muscle of the human body; it helps in bending the hip and the knee and in turning the thigh outwards, the movement of sitting cross-legged. A is wrong because the soleus is a broad calf muscle used in standing and walking. B is wrong because the gracilis, though also a long thigh muscle, is shorter than the sartorius. C is wrong because the trapezius is the large triangular muscle of the upper back and neck. Learn it with the other superlatives: gluteus maximus is the largest muscle, stapedius the smallest and masseter the strongest in force.

The correct answer is D, four. An adult set of thirty-two permanent teeth has eight incisors for cutting, four canines for tearing, eight premolars and twelve molars for grinding, so there is one canine on each side of each jaw. The dental formula of an adult is written as two incisors, one canine, two premolars and three molars in each half of each jaw. A is wrong because three is not a possible number for a feature that is symmetrical on both sides. B is wrong because eight is the number of incisors, and also of premolars. C is wrong because two would mean only one canine in each jaw. Note that a child has twenty milk teeth with no premolars, and that the enamel covering these teeth is the hardest substance in the body.

The correct answer is B, two hundred and six. The adult skeleton has eighty bones in the axial part, that is the skull with the ear ossicles and hyoid, the vertebral column, the ribs and the sternum, and one hundred and twenty-six in the appendicular part, that is the limbs with the pectoral and pelvic girdles, making two hundred and six in all. A is wrong because one hundred and eighty-six matches no division of the skeleton. C is wrong because two hundred and eighty is simply a distractor between the adult and the infant figures. D is wrong for a reason worth remembering: a newborn has about three hundred separate bony elements, and the number falls to two hundred and six as bones such as those of the sacrum, the coccyx and the skull fuse during growth.

The correct answer is A, the stapes. It is the innermost of the three ear ossicles of the middle ear and is shaped like a stirrup; it passes vibrations from the incus to the oval window of the inner ear and is the smallest bone of the body. B is wrong because the malleus, or hammer, is the outermost of the three ossicles, attached to the eardrum, and is larger than the stapes. C is wrong because the patella is the knee cap, a sesamoid bone of moderate size that protects the knee joint. D is wrong because the hyoid is the U-shaped bone of the neck that supports the tongue and is remarkable for a different reason, namely that it articulates with no other bone. The femur, at the other extreme, is the longest and strongest bone.

The correct answer is B, twenty-six. The adult column is counted as seven cervical vertebrae in the neck, twelve thoracic vertebrae bearing the ribs, five lumbar vertebrae in the lower back, one sacrum and one coccyx, giving twenty-six bones in all. A is wrong because twenty-four counts only the separate cervical, thoracic and lumbar vertebrae and leaves out the sacrum and the coccyx. C is wrong because thirty matches no stage of development. D is wrong for the reason that makes this question a trap: a child has thirty-three vertebrae, of which five fuse into the sacrum and four into the coccyx, so the adult number becomes twenty-six. Remember also that the first cervical vertebra is the atlas and the second the axis, and the pivot joint between them turns the head.