How many puppies can you count?

A full-term pregnancy for a dog usually lasts 63 days. At 42 days of pregnancy, the skeletons of the fetuses start to calcify and can just be seen on a radiograph (“x-ray”). By 50-55 days of pregnancy, they are sufficiently visible to be able to count skulls and spines to try to determine litter number. How many puppies is this mom expecting?

The arrows point to 5 skulls. Some of them are obscured by other anatomy in the abdomen. This poor mom needs to have a bowel movement, too!