188 ANATOMY OF THE RABBIT 



vestibuli), lies above and in front of that just described. It is 

 closed by the base of the stapes. 



The auditory ossicles (ossicula auditus) comprise three ele- 

 ments, namely, the malleus, incus, and stapes, which bridge the 

 space intervening between the tympanic membrane and the opening 

 to the internal ear as represented by the vestibular fenestra. They 

 occupy the dorsal angle of the triangular area already described 

 and lie immediately above the promontory. The malleus is the 

 lateral element. The main portion, termed the head, is concealed 

 by the projecting edge of the external acoustic meatus. It bears 

 a stout vertical process, the manubrium mallei, which in the 

 natural condition lies in contact with the tympanic membrane. 

 The incus is the intermediate element; it is directly articulated 

 with the malleus, and bears a downwardly-directed long limb 

 (crus longum), for articulation with the minute head of the stapes. 

 The latter element is a small stirrup-shaped bone, occupying an 

 almost transverse position, and articulated at its base with the 

 margin of the vestibular fenestra. 



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 as it is in man. 



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 sagittal, coronal, 

 squamosal, and lambdoidal. The posterolateral angle of the bone 

 is produced ventrally into a long, curved squamous process (pro- 

 cessus squamosus), which lies in the angle formed by the tentorium 



