306 THE SKELETON OF THE BABBIT. 



border of the nasal bone, and above the 

 maxilla and the anterior process of the frontal. 

 On the under surface of the skull, bounded 

 laterally by the premaxillse and maxillas, 

 and behind by the hard palate, is a large tri- 

 angular aperture, divided longitudinally into 

 the slit-like anterior palatine foramina by 

 the palatal processes of the premaxillffi, a pair 

 of thin longitudinally rolled laminae attached 

 in front to the premaxillffi, and enclosing the 

 organs of unknown function known as Jacob- 

 son's organs. 

 V. Ihejugals or malar s are a pair of laterally com- 

 pressed bars forming the greater part of the 

 length of the zygomatic arches, which bound 

 the orbits below. Their anterior ends are 

 fused with the zygomatic processes of the 

 maxillse, and posteriorly they articulate along 

 their dorsal edges with the squamosals. 



b. Bones in relation with the mandibular arch. 



The uppermost part of the mandibular arch is 

 said to give rise to the incus and malleus, which 

 have already been described in connection with 

 the auditory capsule (p. 303). 

 i. The squamosals are a pair of slightly curved 

 bony plates, which complete the side-walls 

 of the cranial cavity, lying in front of the 

 periotics, and articulating with the parietals, 

 frontals, orbito-sphenoids, and ali-sphenoids. 

 From the hinder border of each squamosal 

 a slender post tympanic process arches back- 

 wards over the external auditory meatus, 

 lying along the outer surface of the periotic. 



From the outer surface of the squamosal 

 arises a stout zygomatic process, which bears 

 on its under surface the articular facet for 

 the mandible : beyond the facet it bends down- 



