Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/34

20 internal ridge marks the boundary between the cerebral and olfactory fossae. The cribriform plate is attached to the frontal bones between the olfactory fossa and nasal cavity.

This highly complicated bone, of cartilaginous origin, is the chief representative of the embryonic nasal capsule. It includes the perpendicular plate of the nasal septum, the cribriform plate, and the ethmoturbinal bones.

The maxillary bone consists chiefly of five processes—the frontal, zygomatic, alveolar, palatine, and orbital. It is a membrane bone. The frontal process is divided by the large infraorbital foramen into a lateral and median portion. The latter forms part of the lateral wall of the nasal cavity and is comparatively thin. The skull is unossified posterior to this part of the frontal process, which joins the premaxillary bone dorsally and anteriorly. The lateral portion of the frontal process is a laterally concave plate connected with the dorsal surface of the cranium by a bony arch. To the dorsal end of this plate is attached the zygomatic process, which forms the anterior half of the zygomatic arch. The alveolar process (so called because it contains the alveoli of the teeth) is a strong bony mass holding the three molar teeth. It is bounded posteriorly and dorsomedially by the sphenoid bones, medially by the palatine process and palatine bone. The palatine process joins its fellow on the opposite side by a median suture in the roof of the mouth. It forms part of the hard palate. In front it surrounds the posterior half of the prepalatine foramen. It joins the pala-