Muscles, Nerves, and Skin

The muscles of giraffes are similar to those of other artiodactyls but differ in order to accommodate the stresses associated with an extraordinary shape. Extensor muscles of the neck are relatively small but flexor muscles of the neck that have to contract against the elasticity of the ligament nuchae are well-developed. The muscle bodies of neck muscles are located at the base of the neck and exert their effects via long tendons, which minimizes neck mass. Giraffes rarely lie down, or sleep, or run. Consequently limb muscles give support more than movement and are more tendinous that muscular. The power to run is generated by hip flexors and extensors, aided by contractions of the gastrocnemius muscles. The forelimb is the main support for body mass and acts as the fulcrum for movement. Chest and forelimb muscles keep the shoulder and elbow joints rigid, but allow drinking and the complications that arise from it. Brain mass forms 0.5% of adult body mass. Eyes are large and the retina has a unique distribution of photoreceptors that provides both clear images of close objects and allows focusing on ground level objects. Peripheral nerves contain more sensory than motor fibers. The skin of giraffes forms ~10% of body mass, and has more collagen than elastic fibers. Skin panniculus muscles are absent, an absence compensated by sebaceous gland secretion of volatile compounds that repel insects. The development of the colors of skin markings begins in the last trimester of pregnancy.