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 =extra-columellar= cartilage which reaches the tympanic membrane. The lower process of this extra-columella 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 extra-columella are together homologous with the chain of mammalian auditory ossicles.
The =Optic capsules= and associated bones.
Two pairs of bones are associated with the optic capsules, viz. the _lachrymals_ and the _supra-orbitals_. The _lachrymal_ (fig. 44, 3) is a fairly large flattened bone lying wedged in between the maxillae, nasal, jugal, and prefrontal. It forms a considerable part of the anterior boundary of the orbit, and is pierced by two foramina. On the orbital edge is a large hole leading into a cavity within the bone which lodges the naso-lachrymal sac, and communicates with the narial passage by a wide second foramen near the anterior end of the bone. The _supra-orbital_ is a very small loose bone lying in the eyelid close to the junction of the frontal and prefrontal.
The =Olfactory capsules= and associated bones.
Two pairs of membrane bones, the _vomers_ and _nasals_, are developed in association with the olfactory organ, but the =mesethmoid= is not ossified.
The _vomers_ form a pair of delicate bones, each consisting of a vertical plate (fig. 45, 15), which with its fellow separates the two narial passages, and of a horizontal plate which forms much of their roof. The vomers articulate with one another and with the pterygoids, palatines, and maxillae.
The _nasals_ (fig. 45, 2) are very long narrow bones extending along the middle line from the frontal almost to the anterior nares. They are continuous laterally with the premaxillae, maxillae, lachrymals and prefrontals. They form the roof of the narial passages.
3. THE UPPER JAW AND SUSPENSORIAL APPARATUS.
These are enormously developed in the Crocodile and are firmly united to the cranium. It will be most convenient to begin by describing the bones at the anterior end of the jaw and to work back thence towards the brain-case. The most anterior bones are the _premaxillae_. The _premaxillae_ (figs. 44 and 45, 1) are small bones, each bearing five pairs of teeth, set in separate sockets in their alveolar borders. They constitute almost the whole of the boundary of the =anterior nares=, which are confluent with one another and form a large semicircular opening in the roof of the skull, leading into the wide narial passage. They are also partially separated from one another in the ventral middle line, by the small =anterior palatine vacuity= (fig. 43, A, 8). They form the anterior part of the broad =palate=. The alveolar border on each side between certain of the teeth is marked by pits which receive the points of the teeth of the other jaw. The first pair of these pits in the premaxillae are often so deep as to be converted into perforations. Pits of the same character occur between the maxillary and mandibular teeth.