The lumbrical muscles do not attach to the proximal phalanx directly, but rather connect the tendons of flexor digitorum profundus (below, ie volar) to the extensor tendons (above, ie dorsal) and produce flexion by pulling on the extensor tendons as they pass over the proximal phalanx.
By the time they are 12 months old, most babies can weigh three times what they weighed at birth and gain about an inch per month in length. The average infant at one year may be between 2630 inches long. Social and Emotional Development-Infants respond when you say their name. They begin to fear strangers.
Head and trunk control ( infant lifts head, watches a moving object by moving the head from side to side - occurs in the first few months after birth. Infant rolls over turning from the stomach to the back first, then from back to stomach - four or five months of age. Sit upright in a high chair (requires development of strength in the back and neck muscles)-four to six months of age. Infant gradually is able to pull self into sitting positions.