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.
While you can prop your baby in a sitting position almost from day one, sitting independently doesn't begin until your baby has head control. Three months to four months. Your baby's neck and head muscles are strengthening rapidly. From this time she'll learn to raise and hold her head up while she's lying on her tummy.