The vomers (15) are delicate bones articulating with the maxillæ, the palatines, the pterygoids, and with each other. They form a part of the septum and roof of the nasal passage.
The mesethmoid is not ossified.
Reynolds describes the bones of the auditory capsules as follows:
“Three bones, the epiotic, 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 epiotic similarly becomes united with the supraoccipital, the pro-otic ([Fig. 23], 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. 21], 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. 23], 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. The opening of the fenestra ovalis is in the fresh skull occupied by the expanded end of the auditory ossicle, the columella, whose outer end articulates by a concave facet with a trifid extracolumellar cartilage which reaches the tympanic membrane. The lower process of this extracolumella passes into a cartilaginous rod which lies in a canal in the quadrate and is during life continuous with Meckel’s cartilage within the articular bone of the mandible.
“The columella and extracolumella are together homologous with the chain of mammalian auditory ossicles.”
The Lower Jaw
([Figs. 21], [23], and [24]). The mandible consists of two similar rami, rather closely united at the anterior-median symphysis with each other. Each ramus consists of six bones.
The dentary ([Figs. 23] and [24], 18; [Fig. 21], 20) is a long bone that unites at the symphysis with its fellow to form the point of the jaw. It bears, along its dorsal edge, about twenty teeth; all but the posterior four or five of these teeth are in individual sockets; this may vary somewhat with age. The outer surface of the dentary, especially towards the symphysis, is covered with numerous, small, deep pits, while along its inner side, parallel to the row of teeth, is a row of somewhat larger pits like those noted in the maxilla and premaxilla. Articulating with the mesial side of the dentary along the greater part of its length is a flat bone, the splenial ([Figs. 23] and [24], 19); between these two bones is a long cavity that makes the ramus hollow almost to the symphysis. A large foramen, not shown in any of the figures, leads through the splenial into this cavity.
Articulating with the caudal end of the splenial and forming the anterior border, as seen from the mesial side, of the large external mandibular foramen ([Fig. 23], 27) is a small bone, the coronoid ([Figs. 23] and [24], 23, [Fig. 21], 21); it articulates with the splenial anteriorly, with the supra-angular dorso-caudally, and with the angular ventrally.