. Chordate morphology. Morphology (Animals); Chordata. anterior margin of the orbit). Frequently in the cat, a small exposure of ethmoid forms the orbit wall between the frontal and lacrimal. The alisphenoid is excluded from contact with the frontal by the large orbitosphenoid in the rabbit. Ante- rior to the orbit the frontal sutures with the maxilla (in front) and nasal (above). The nasals are paired splints of bone lying above the nasal passages. They contact the frontals posteriorly and the max- illae and premaxillae laterally. They form a part of the margin of the external narial opening.
. Chordate morphology. Morphology (Animals); Chordata. anterior margin of the orbit). Frequently in the cat, a small exposure of ethmoid forms the orbit wall between the frontal and lacrimal. The alisphenoid is excluded from contact with the frontal by the large orbitosphenoid in the rabbit. Ante- rior to the orbit the frontal sutures with the maxilla (in front) and nasal (above). The nasals are paired splints of bone lying above the nasal passages. They contact the frontals posteriorly and the max- illae and premaxillae laterally. They form a part of the margin of the external narial opening. The lateral and ventral margins of the external narial opening are formed by the premaxillae (singular pre- maxilla) bearing the teeth called incisors (three on each side in the cat and dog; two pairs, one in front of the other, in the rabbit). The premaxillae form the anterior part of the palate. The slim palatal processes meet along the midline between the large anterior palatine fenestrae. These proc- esses in the rabbit do not contact the maxillae but meet a downward projecting process of the vomers. Behind the is the maxilla. Each bears teeth. In the cat or dog there is a large canine anteriorly. In front of the canine there is a gap in the tooth row called a diastema into which the canine of the lower jaw fits. Behind the canine are "shearing teeth," three (premolars) in the cat and four (premolars) in the dog. The most posterior of these teeth in both animals is called a carnassial tooth, since its cutting edge matches that of a tooth in the lower jaw in such a way that they function like scissors. The other shearing teeth pass between each other, cutting by means of a slid- ing action. The dog has two molars behind the carnassial. The cat has one. The rabbit lacks incisors and has six peg-like teeth in each maxilla; its formula is 1 Vi, C %, P %, M %. The formula indicates the number of incisors (I) in the upper jaw over the number in the
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