Northern Renaissance painters were less concerned with physical anatomy than their Italian counterparts.
The figures in Northern Renaissance paintings are covered in heavy layers of clothing that didn't require the artists to have a deep understanding of the human body. Such portrayals were also because much of the artwork from the Northern Renaissance is religious.
The paintings depicted well-known Biblical scenes and were showcased in churches. Exposing the human body would not have been considered appropriate in this setting. 
Religious figures were placed in contemporary 15th or 16th century clothing to make the individuals more relatable to the audience.
Clothing was used to portray status, wealth, and divinity. For example, the Virgin Mary was seen exclusively in deep red or blue in paintings. Blue to show purity and red to show her femininity. Furthermore, the use of color to display texture, such as velvet or silk, in portraits, was used to show the status of the individual being painted. 
Oil painting gave the artists the ability to be extremely detailed in the construction of clothing and, when appropriate, the construction of the human body. More emphasis was placed on the clothing, detail, and symbolism than the physical anatomy.