The musculature of the mystacial vibrissae of the white mouse.

Striated muscles of the mystacial region of the common albino mouse have been described. They were divided into two categories: extrinsic and intrinsic. The four extrinsic muscles (m. levator labii superioris, m. maxillolabialis, m. transversus nasi, m. nasalis) belong to the facial muscles. They originate on the skull and insert into the corium between the mystacial vibrissae. Their contraction moves the whole mystacial region in directions dependent on their origins. Intrinsic (follicular) muscles are associated solely with the vibrissal follicles and have no bony attachment. They were found around follicles alpha, beta, gamma, delta, around all follicles of rows A and B, and around the first six follicles of rows C, D and E. The form of the follicular muscle is a sling connecting two adjacent follicles of the same row. The arc of the sling surrounds the inferior part of the rostral follicle and the two extremities insert to the conical body of the caudal follicle and to the neighbouring corium. They are the protractors of the vibrissae. The inferior parts of the vibrissal follicles of a given row are fixed in a fibrous band which inserts in the anterior part of the muzzle. It is proposed that these bands become stretched during the protraction of vibrissae and contract, by their elasticity, immediately upon the end of the follicular muscles' contraction, executing the fast return of vibrissae to their resting, retracted position.