Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/35

Rh tine bone posteriorly. The orbital process overlaps the anteroventral portion of the frontal bone's orbital process. It forms but a small part of the wall of the orbito-temporal fossa. A pronounced longitudinal groove on the floor of the fossa partly separates the orbital from the alveolar process.

The lacrimal bone is a thin inconspicuous element, of membranous origin, lying on the dorsomedial wall of the infraorbital foramen. It is immediately below the bony arch which connects the dorsal surface of the skull with the lateral part of the maxillary bone's frontal process. The bone is easily overlooked if its sutures are not exposed by careful scraping.

The premaxillary bone, of membranous origin, forms the anterior part of the upper jaw, and the lateral and ventral walls of the front part of the nasal cavity. With the nasal bone it surrounds the anterior nares. Its frontal process is thrust dorsally between the nasal and maxillary bones, extending caudally to the frontal bone. This process is partially overlaid laterally by the maxillary bone. On the ventral side the palatine process extends horizontally across the roof of the mouth, surrounding the anterior part of the prepalatine foramen and meeting its fellow at a median suture. This suture extends backward between the two maxillary, as well as between the palatine bones. The premaxillary bears an enormous incisor tooth. Carefully chip away the bone surrounding this tooth, and note the size and shape of the alveolus. The palatine process joins the palatine process of the