94 Anatomy or the Rabbit. 



dinal excavation, the maxillary sinus (sinus maxillaris), widely open 

 to the nasal fossa, but only seen to advantage when the ethmoturbinal 

 is removed. The lateral wall of the sinus corresponds in position with 

 the fenestrated area of the external surface. It bears the chief part of 

 the nasolacrimal canal. 



The alveolar process (processus alveolaris) is that portion of the 

 maxilla lodging the sockets of the cheek-teeth. In the rabbit it is 

 separated by the diastema, in which no teeth occur, from a corresponding 

 but imperfectly differentiated process of the premaxilla. 



The palatine process (processus palatinus) extends toward the median 

 plane. It forms with its fellow of the opposite side about two-thirds of 

 the palatine bridge. 



The orbital process (processus orbitalis) is directed obliquely toward 

 the dorsal surface of the skull. In conjunction with the lacrimal bone 

 and the maxillary process of the frontal, it forms the anterior orbital 

 rim. It is continuous with the fenestrated portion of the body, and its 

 appearance as a process is largely due to its solid character as com- 

 pared with the perforated surface lying in front of it. 



The zygomatic process (processus zygomaticus) forms the anterior 

 root of the zygomatic arch, and in the adult condition has fused with it 

 the anterior end of the zygomatic bone. Its ventral angle bears a 

 prominent masseteric spine for the attachment of the ligament of the 

 masseter muscle. 



The sphenoorbital process (processus sphenoorbitalis) lies on the 

 medial wall of the orbit, in a position opposite to the middle portion of 

 the ridge lodging the posterior cheek-teeth. It forms a stout buttress, 

 the tip of which is applied to the anteroventral angle of the frontal bone. 

 In this position it is visible from the orbit, lying between the lacrimal 

 bone and the ethmoidal process of the orbitosphenoid. 



13. THE PREMAXILLA. 



The premaxilla, or incisive bone (os incisivum), forms the anterior 

 portion of the upper jaw. It comprises a central portion, the body — 

 including with the latter the scarcely differentiated alveolar portion con- 

 taining the large and small incisors — a frontal process, and a palatine 

 process. The body forms a portion of the palatal surface of the skull 

 and of the lateral boundary of the incisive foramen. Its dorsal surface 

 forms part of the boundary of the piriform aperture, the remaining por- 

 tion of this being formed by the nasal bone. The palatine process extends 

 backward on the medial side of the bone, closely applied on the palatal 

 surface to its fellow of the opposite side, and forms in this way a medial 

 boundary for the incisive foramen. Its dorsal surface, in conjunction 

 with that of the corresponding process of the other side, bears a broad 

 palatine groove (sulcus palatinus), lodging a portion of the cartilage of 

 the vomeronasal organ and nasopalatine duct. The frontal process (pro- 

 cessus frontalis) is a thin bony splint, extending backward between the 

 nasal and maxillary bones, and terminating between the former and the 

 maxillary process of the frontal. 



