The Chondrocranium of Calotes versicolor (Daud.) with a Description of the Osteocranium of a just-hatched Young

Abstract

ABSTRACT 1. In the earliest stage of Calotes studied, the basal plate is confluent with the pleurocentrum of the atlas and axis vertebrae. Later, a joint appears between the hypocentral condyle and the first vertebra. This shows that, at least temporarily, the elements of the anterior sclérotomie half in this region are in continuity with the posterior in front as happens in the vertebral region. The occipito-atlantic joint is, therefore, intravertebra! and intersegmental as in other Lacertilia. 2. The anterior semicircular canal is completely separated for a short distance from the remaining otic capsule. The gap is filled with connective tissue. 3. The intervestibular septum shows a lateral foramen which transmits nothing and the utricular connexion between the anterior and posterior chambers passes posteriorly to the median part of the septum and, therefore, a medial orifice is not formed. 4. The preoptic roots, the orbital cartilages, and metoptic pila are paired in early stages; the orbital cartilage connects the preoptic root, pila metoptica and pila antotica dorsally. Later the two preoptic roots merge to form a median preoptic pillar, the orbital cartilages anteriorly unite to form the planum supraseptale, while posteriorly also the orbital cartilages (taenia medialis) unite at the region of the hypophysial foramen. This posterior united portion is met by a median vertical pillar (formed by the fusion of cartílago hypochiasmatica, subiculum infundibuli, and pilae metopticae) arising from the trabecula communis. The single septal fenestra is divided into an anterior larger and a posterior optic by the formation of median interorbital pillar from the ventral interorbital septum which meets the posterior portion of the planum supraseptale. The ventral portion of the interorbital septum is never noticed to be paired ; the taenia marginalis is absent. However, short projections from the posterodorsal margin of the planum and from the anterodorsal face of the otic capsule represent the reminiscence of marginalis connexion. A supratrabecular bar is absent. 5. In the nasal capsule, a concha nasalis is absent ; therefore, the lateral nasal glands are unenclosed in a cartilaginous capsule. The anterior portion of the paranasal cartilage unites with the dorsal portion of the lamina transversalis anterior, and the latter gives rise to an ectochoanal cartilage, but a paraseptal cartilage is absent. On the ventral side, from the free median margin of the lamina, orbitonasalis, there arises a short projection which represents the posterior portion of the paraseptal cartilage. 6. The pterygoquadrate shows a free streptostylic quadrate, a processus ascendens which ossifies into the epipterygoid, a processus pterygoideus only in early stages, a basipterygoid articulation by a free meniscus cartilage, and an otic articulation with the crista parotica and processus paroticus by the quadrate. 7. The columella auris shows a ligamentary processus dorsalis connexion with the processus paroticus, a cartilaginous processus internus which articulates with the quadrate, a processus accessorius anterior which is connected with the quadrate by a ligament, and a ligamentary connexion between the pars superior of the insertion plate and processus paroticus. The processus accessorius posterior-ceratohyal connexion was not noticed. There is also a muscle (a part of M. stylohyoid) spanning the pars superior and crista parotica. The pars superior-paroticus ligamentary connexion, with the chorda tympani running laterally to it, is homologized with the laterohyal of Sphenodon and the crocodile. 8. The hyoid apparatus shows a processus, lingualis and cornuhyale (paired hypo-and ceratohyals) arising from a median basihyal and two pairs of ceratobranchials. 9. In the osteocranium, the oto-occipital of each side is formed by the fusion of opisthotic and exoccipital, while the supraoccipital is formed by an ossification in the tectum and its fusion with the two epiotics formed in the sinus region of the otic capsule. The basioccipital and the composite ‘sphenoid’ are not united. The pleurosphenoid ossifies in the pila antotica. The epipterygoid is connected at its dorsal end with the parietal by a ligament, and ventromedially it is free from the meniscus cartilage. The frontals and parietals are paired in the stage examined, and in the adult the parietals of each side fuse, as also the frontals.