Fine Structure of the Sinus Hair (Pillus labialis maxillaris) and its Microvascular Architecture in the Cat

: The hairs of the upper lip are designated as the sinus hairs morphologically and as the tactile hairs functionally. The characteristics of the sinus hair include the equipment of a follicular blood sinus, composed of cavernous and ring sinuses located between the external and internal radical dermal capsules. The present paper deals with microvascular architectures examined under SEM using plastic microvascular casts. The arterioles diverging from the superior labial artery divided into two groups near the external capsule. The radical arterioles passed through an opening at the bottom of the capsule and formed the capillary network of the hair papilla, in part communicating with the network of the radical dermal capsule. The subcapsular arteriole penetrated the external capsule and passed in the cavernous sinus up to the internal capsule, where the capillary network of the radical dermal capsule was formed. Its meshes appeared polygonal of the papilla site and elongated at the epithelial site. The follicular blood sinus extended between the sebaceous gland and the papilla radix of the sinus hair. In its papillary two-thirds, the cavernous sinus was formed by connective tissue trabeculae and in the epithelial one-third the ring sinus was formed in the shape of a doughnut without trabeculae. Locational differences in the meshes of both networks of the hair papilla and the radial dermal capsule were apparent according to the extent of the nutrient supply to the internal and external root sheathes. The follicular blood sinus acted as a reducing apparatus against the external forces pressing on the sinus hair and the cavernous sinus may serve to enhance the function of the tactile apparatus.