The development of the second branchial arch (Reichert's cartilage), facial canal and associated structures in man.

T HE present article reports, primarily, observations on the development of the facial canal, with special reference to the second arch ofthe primitive branchial skeleton and to the nature of the tissue enveloped by the canal in the course of its closure. Secondarily, t he study i concerned with concurrent steps in morphogenesis taken by the auditory ossicles (with their muscles and ligaments), t he otic capsule, the pyramid for t ransmission of the stapedial tendon and the semicanal which houses t he tensor tympani. Related to all of the above-named elements is the mucoperiosteal membrane, which, in its spread, invests t he auditory ossicles and the muscles and nerves on the tympanic wall of the otic capsule. Complexity in the process of development of the facial canal is owing chiefly to the fact that the otic capsule, which contributes largely to t he wall of the canal, is a composite structure--being formed from as many as fourteen originally separate ossification centers. In terms of morphogenesis of t he facial canal, this circumstance means t hat the capsular wall cannot develop at t he same