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.
What to do if your baby doesn't sit up. If your baby isn't able to hold his head up steadily by the time he's about 4 months old and hasn't started learning to prop himself up on his arms shortly after that or is unable to sit by 9 months, bring it up the next time you talk to his doctor.hile you can prop your baby in a sitting position almost from day one, true independent sitting doesn't begin until he has head control. Starting at about 4 months, your baby's neck and head muscles strengthen rapidly, and he'll learn to raise and hold his head up while he's lying on his stomach.