Posts Tagged ‘Bicuspid’

Basic Anatomy

Sunday, February 14th, 2010


In this section I have tried to outline the more important elements used in establishing a system of effective classification and at the same time to enlighten the layman to the “little things” that are a very important part of making a lizard a lizard. Although this chapter is brief, it is as complete as space allows and as accurate as possible.

Skull

In general discussions about the head of an animal, the upper portion is referred to as the cranium, while the lower part consists of the mandible. In lizards the foremost bone of the mandible is the dentary; it is at the foremost point of the dentary bone that the two halves of the mandibles are firmly united (the symphysis). The mandible articulates with the cranium at the quadrate bone, located near the rear of the cranium. The coronoid bone juts up behind the dentary bone and fits into a socket formed by the pterygoid bones of the cranium. The distance from the tip of the snout to the coronoid intersection determines the gape of the lizard.

In the mandible, teeth are found on the dentary bone; in the cranium they may be on the maxillary, premaxillary, palatine, or pterygoid bones. The teethe themselves may be pleurodont (along the side of the bone) or acrodont (along the crest of the bone). On some lizards thecodont teeth (fitting into sockets) are found, but along with one of the other types. The teeth may be pyramidal, conidal, flat, bicuspid, or tricuspid. They can be quickly and frequently replaced.

Between the maxillary, premaxillary, and septomaxillary, bones is a large gap in the cranium. This is in effect the internal nasal arch through which the nostrils draw air through the skull into the mouth. Another gap exists a little behind this.

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Dentary Bone

Tuesday, January 13th, 2009


In the mandible , teeth are found on the dentary bones; on the cranium they may be on the maxilliary, premaillary  , palatine or pterygoid bones.  The teeth themselves may be pleurodont ( along the side of the bone) or acrodont ( along the crest of the bone).  In some lizards theodont teeth ( fitting in the sockets) are found, but along with one of the other types.  The teeth may be pyramidal , conical , flat , bicuspid or tricuspid.  They can be quickly and frequently replaced.

Between the maxilliary, premaxilliary and septomaxilliary bones is a large gap in the cranium.  This is in effect the internal nasal arch through which the nostrils draw air through the skull into the mouth.  Another gap exists a little behind this , usually behind the middle of the skull , and in here that the eye is housed.  Along the ocular cavity is a bone or pair of bones , called the frontals.  This is a centrally located bone met anterior by the nasals or occasionally the prefrontal.  It is bordered posterior by the parietal.  Along the border of the frontal and parietal , or often in the center of the parietal. may be found a single round eye. It is this small aperature that may be the pineal gland or  “third eye” is located.  In species lacking the eye. this pineal foramen is often absent.

There may be a temporal arch, an arch of bone created by the postorbital and squamosal bones.  The lower arch . formed by an extension of the jugular with the quadrate. is not generally found in lizards , but does occur in tuarta, Sphendodon, a lizard like animal inhabitant of New Zealand.  In some lizards and all snakes the upper temporal arch is lacking; in these forms the squamosal bone is rudimentary or absent.

Richard Dawkins – Children in the Atheist’s Den, part 3 of 8 – “One point of uncertainty was the angle at which the face attached to the cranium. Alan Walker remembers an occasion when he, Michael Day, and Richard Leakey were studying the two sections of the skull. ‘You could hold the maxilla …

Imported Fire Ants Glossary – reptile: any of a group of cold-blooded air-breathing vertebrates, such as snakes, lizards, turtles and alligators, that usually lay eggs and have skin covered with scales or bony plates. scape: the basal segment of the antennae …

The Pineal Gland, LSD, and Serotonin — Updated: October 15, 1996 – The parietal nerve leaves the retina, passes through the capsule, and courses posteriorly under the roof of the cranium and then ventrally to the epiphysis and brain. [9] We know that the parietal eye is functional because there are …

A Theory For The Birds – No larger eyes (almost filling up the cranium), and no coordinating system to OPERATE all these complex systems. Let’s understand. You can have an entire plane — but rip out the controls and instrument panel and the plane will be of no …

Upper Deck Entertainment Forums – Fish Guide (YES its a guide) – I opted to not use Cranium Fish, as I personally feel that Golden Flying Fish is more effective… While they both have their advantages, if you mix Golden Flying Fish with Superancient, and swarm Oyster Meister, thats 6 cards instantly …

trip to science centre, and comex fair – parasaurolophus, a hadrosaur (duck-billed reptile with curved crest across cranium). stegosaurus, largest of the stegosaurids. allosaurus, a carnosaur from the jurassic period. dilophosaurus, a slender carnivore with crests on head, …

 

One last aspect of the skull , that should be mentioned and covered is the occipital condyle. the point where the cranium is fixed to the skull.  This is a point of bone ( single in lizards and other reptiles) where the first vertebra, the atlas attaches to the skull.  It is not always the hindmost part of the skull.

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