2 Months

• At two months the Babinski reflex should occur.infant image by Mykola Velychko from Fotolia.com
  
  At two months primitive muscle development has occurred in the infant. Simple reactions occur such as the Babinski reflex, where the toes will fan outward when the sole is tickled. Another simple reaction that occurs by two months is the palmar hand grasp, where the infant will "grasp" another individual's finger. The infant can lift and turn the head when laying on its back, but neck is still unable to support the head.
  
  

3 to 4 Months

• At three months the infant has enhanced eye control.krank image by Herbie from Fotolia.com
  
  At three to four months the infant has enhanced eye control and is able to follow the movement of an object. As of this point the infant is unable to fully coordinate movements, but is beginning to make efforts. When laying on its stomach the infant is now able to raise itself up and the neck muscles are strong enough to support the head.
  
  

5 to 6 months

• At six months the infant can support its head and sit upright.aufschauen image by Sandro G??tze from Fotolia.com
  
  At five to six months the infant should be able to sit upright on its own for up to 30 seconds or more. It is now able to grasp objects using ulnar-palmar grasping, but does not yet use thumb opposition. Muscles in the back and legs have developed to allow the infant to roll from back to tummy.
  
  

6 to 9 Months

• Between six to nine months the infant may be able to crawl.crawling champ image by Yoram Astrakhan from Fotolia.com
  
  Between six to nine months crawling may begin. When supported, the infant should be able to walk short distances. By now the infant can sit unsupported for much longer periods of time. It will learn to sit down from a standing position and even pull itself into a standing position. After nine months the infant will begin to balance while standing alone and take its first steps.
  
  

Differences in Male and Female Infants

• Overall, the muscular development of male and female infants is identical. It is not until individuals reach puberty that muscular development is differentiated. Population, individual, and cultural differences can affect the timing of muscular development milestones in male and female infants. Some cultures show a slight advantage in small muscle development in females, such as lip and tongue articulation. Female infants also have laxer ligaments, due to the presence of female hormones.