Top definition. Musk. Though technically the name for the secretion of the male musk deer, musk is most often used as the name for the scent of arousal in both men and women, as actual musk is used in perfumes and colognes. Generally causes arousal for both genders, as it is a secondary sex characteristic.
These photoreceptors are called the rods and cones. Rods are called rods because under the microscope, they are shaped like, of all things, a rod. Finally, those pesky scientists named a structure for what it actually looks like as opposed to someone's unpronounceable last name!
The retina contains 100 million rods and 7 million cones. The retina is lined with black pigment called melanin -- just as the inside of a camera is black -- to lessen the amount of reflection. The retina has a central area, called the macula, that contains a high concentration of only cones.