Each _prefrontal_ (fig. 45, 14) forms part of the inner wall of the orbit and sends ventralwards a process which meets the palatine.
The _postfrontals_ (fig. 44, 6) are small bones lying at the sides of the posterior part of the frontal. Each is united with a number of bones, on its inner side with the frontal and parietal, behind with the squamosal, and ventrally with the alisphenoid. It also unites by means of a strong descending process with an upgrowth from the jugal, and thus forms a =postorbital bar= separating the orbit from the lateral temporal fossa. The postfrontal forms also part of the outer boundary of the supratemporal fossa.
Skeletal capsules occur in connection with each of the three special sense organs of sight, of hearing and of smell.
The =Auditory capsules= and associated bones.
Three bones, the =epi-otic=, =opisthotic= and =pro-otic=, together form the auditory or =periotic= capsule of each side. They are wedged in between the lateral portions of the occipital and parietal segments and complete the cranial wall in this region. Their relations to the surrounding structures are very complicated, and many points can be made out only in sections of the skull passing right through the periotic capsule. The relative position of the three bones is, however, well seen in a median longitudinal section. The =opisthotic= early becomes united with the exoccipital, while the =epi-otic= similarly becomes united with the supra-occipital, the =pro-otic= (fig. 45, 7),--seen in longitudinal section to be pierced by the prominent =trigeminal foramen=--alone remaining distinct throughout life. The three bones together surround the essential organ of hearing which communicates laterally with the deep tympanic cavity by the =fenestra ovalis=.
The =tympanic cavity=, leading to the exterior by the =external auditory meatus= (fig. 44, 16), is well seen in a side-view of the skull; it is bounded on its inner side by the periotic bones, posteriorly in part by the exoccipital, and elsewhere mainly by the quadrate. A large number of canals and passages open into it. On its inner side opening ventro-anteriorly is the =fenestra ovalis=, opening ventro-posteriorly the =internal auditory meatus= (fig. 45, VIII), while dorsally there is a wide opening which forms a communication through the roof of the brain-case with the tympanic cavity of the other side. On its posterior wall is the prominent foramen through which the facial nerve passes on its way to its final exit from the skull through the exoccipital, this foramen is bounded by the quadrate, squamosal, and exoccipital.