• 1A study has been made of the maxillary nerve in eighty-three specimens of nineteen species of placental mammals. The series included representatives of six mammalian orders.
  • 2In this material, the maxillary trunk first gives off the zygomatic nerve and then passes forwards on the orbital floor. It gives origin to the posterior and anterior superior dental nerves, and splits at a variable point into nasal and labial divisions. The nasal division supplies the surface of the snout, the rhinarium and the vestibule of the nose, frequently giving twigs to the uppermost members of the group of mysticial vibrissae. The labial division is distributed to the remainder of the mysticial vibrissae, and to the skin of the cheek and upper lip.
  • 3If the rhinarium or the uppermost mysticial vibrissae are prominent, the nasal division is correspondingly big.
  • 4If the lower members of the group of mysticial vibrissae are well developed, it is the labial division that is relatively enlarged.
  • 5The relative sizes of the facial branches of the infraorbital nerve are also affected by the development of specialized facial features—e.g. in the pig the vast majority of nerve fibres are distributed to the disc-like ending of the snout.
  • 6Certain structures presumably derived from the frontonasal process receive their nerve supply from the nasal division, while those derived from the maxillary processes are normally supplied by fibres from the labial division. In the ungulates, however, the nerve supply to the mobile upper lip is derived from branches of the nasal division.