Which layer is absent in the dog's planum nasale that typically exists in other skin regions?

The planum nasale, or the moist surface of the dog's nose, has a unique anatomical structure when compared to typical skin. One of the distinguishing features of the planum nasale is the absence of the stratum granulosum, a layer commonly present in the epidermis of other skin regions.

The stratum granulosum is primarily characterized by the presence of keratinocytes that undergo a process of keratinization, where they accumulate keratohyalin granules as they begin to die and form a tougher barrier. This stratum plays a significant role in creating a water-resistant layer in typical skin. However, in the planum nasale, the skin is adapted to remain moist and does not require this additional barrier layer.

In areas where the stratum granulosum is absent, the skin features a thinner overall epidermis, allowing for better sensory functions and moisture retention, which are particularly important for the nose's sensory and thermoregulatory roles in dogs. This unique adaptation emphasizes the structural and functional differences between the planum nasale and other skin areas, reflecting its specialized purpose.