The Bones of the Skull. 149 



7. THE INTERPARIETAL BONE. 



The interparietal (os interparietale) is a small, lozenge-shaped 

 element, surrounded by the two parietal bones and the supra- 

 occipital. It is the first of the membrane roofing elements of the 

 cranium proceeding forward from the supraoccipital, and in the 

 rabbit's skull is not fused with the occipital segment. 



8. THE PARIETAL BONE. 



The parietal bone (os parietale) is a characteristic roofing bone 

 covering a large portion of the middle cranial fossa. It is somewhat 

 rectangular in shape, and is, connected by serrate sutures with the 

 surrounding elements and with its fellow of the opposite side, the 

 sutures producing a characteristic pattern on the external surface 

 of the skull. The sutures are medial, anterior, lateral, and posterior 

 in position, and are designated respectively as saggital, coronal, 

 squamosal, and lambdoidal. The posterolateral angle of the 

 bone is produced ventrally into a long, curved squamous process 

 (processus squamosus), which lies in the angle formed by the ten- 

 torium cerebelli and the lateral wall of the middle cranial fossa. 

 It is not exposed to the external surface of the skull. 



9. THE FRONTAL BONE. 



The frontal bone (os frontale) is a paired element, lying 

 directly in front of the parietal, and forming with its fellow of the 

 opposite side the anterior portion of the roof of the cranial cavity 

 and also a considerable portion of its lateral, orbital wall. Unlike 

 the condition in the human skull, the two bones are separate 

 throughout life, so that there is a permanent frontal SUture. 

 Each consists of a frontal portion (pars frontalis) , the external or 

 dorsal surface of which continues that of the parietal, and of an 

 orbital portion (pars orbitalis), enclosing the dorsal portion of 

 the orbit. The two parts are connected at the supraorbital 

 border, with which is also connected the base of the divided 

 supraorbital process. The anterior end of the frontal portion 

 is deeply notched where it comes in contact with the nasal and 



