The Development of the Osteocranium of the Egyptian Cobra

Abstract

AbstractIn the present article, the median dorsal bones, bones of the upper jaw, circumorbital series and occipital ring of the skull of the adult Egyptian cobra, Naja haje have been described in detail, and compared with those of the other snakes studied by the previous authors. The median dorsal bones of the cranium are the nasals, frontals, parietals, but not the premaxillae. The paired nasals are exceptionally elongated anteriorly to the extent that the premaxillae and their processus nasalis are completely hidden in a dorsal view. The paired frontals send lateral downgrowths through their whole length which unite together in the mid‐ventral line just dorsal to the parasphenoid. The fused parietals also send lateral downgrowths which articulate ventrally with the posterior part of the parasphenoid and the anterior part of the basisphenoid.The upper jaw is composed only of the premaxilla, maxilla and quadrate on either side. The fused premaxillae possess a processus nasalis, and ventrally they send backwards a palatal process. The maxilla carries two poisonous fangs and two solid small teeth. It is quite separate from the premaxilla, but connected with the palatine (through its palatal process), prefrontal and ectopterygoid. The length of the maxilla is reduced in comparison with that of the boids and colubrids.The incomplete bony orbital ring is formed only of the prefrontal, frontal and postfrontal. Thus the jugal, lacrymal and postorbital are completely lacking, and the parietal is excluded from the circumorbital series by the presence of the postfrontal. The prefrontal extends from the cranial roof to the upper jaw. It is firmly fixed dorsally with the antero‐lateral border of the frontal. Its ventral edge is firmly fixed to the dorsal surface of the maxilla and its palatal process. The antero‐dorsal edge of the postfrontal is connected with the postero‐lateral edge of the frontal, while its medial edge is in sutural contact with the parietal and its lateral downgrowth.The occipital ring consists of the four occipital bones; the basioccipital ventrally, the two exoccipitals laterally and dorsally, and the supra‐occipital dorsally. The sutures separating these bones from one another are distinct. The two exoccipitals articulate with each other dorsally above the foramen magnum, thus excluding the supraoccipital from this foramen. The occipital condyle is tripartite formed out of the basioccipital and the two exoccipitals. The exoccipital is completely fused, without any line of demarcation, with the opisthotic to form a compound bone which is called the otoccipital.