![]() On each side, the neural arch carries an outwardly directed transverse process. On the roof of the neural arch is a low median ridge, the neural spine or spinous process. Dorsally, the centrum bears a bony ring, the neural arch, which encloses the spinal cord in a neural canal. It is composed of a series of ten separate bones, the first nine of which are the ring like vertebrae and the last is a long rod-like urostyle (oura = tail styles rod).Ī typical vertebra, taken from the middle of the series, consists of a solid cylindrical part, the body or centrum, which is concave in front and convex behind and therefore said to be procelous (pro = front coel=hollow). The vertebral column is situated dorsally and extends from the base of the skull to the posterior end of the trunk. Each capsule is a cartilaginous box which is covered over by a single cartilage bone called pro-otic. The auditory or otic capsules are situated posteriorly, one on each side of the cranium, just in front of the ex-occipitals. The cartilaginous optic capsules are not fused with the cranium and therefore they are not found in a prepared skeleton. The orbits are represented by two large cavities, one on each side of the cranium. Each half of the nose is covered over by a triangular membrane bone called nasal, and its floor is supported by another membrane bone, the vomer. The nasal capsules are attached to the anterior end of the cranium and the sphenethmoid extends into them from behind. Besides the foramen magnum, the brain case is perforated by several small openings for the exit of the cranial nerves. At the anterior end of the cranium is a ring-like cartilage bone, the sphenethmoid, which is completely covered over by the front parietals. The floor of the cranium is supported by a dagger-shaped Para sphenoid, the blade of which points forwards. The roof of the cranium is formed by a pair of thin flat bones called front parietals which extend from the ex-occipitals behind to the nasal capsules in front. The two occipital condyles fit into depressions on the first vertebra. The foramen is bordered on each side by a cartilage bone called ex-occipital, which bears a convex occipital condyle. This is the foramen magnum (foramen=bore) through which the brain joins the spinal cord. It is tubular in shape and pierced by a large hole at the posterior end. The cranium forms the narrow central part of the skull. (vii) The hyoid apparatus, supporting the floor of the mouth cavity. (vi) The lower jaw, which is movably articulated to the upper jaw and (v) The upper jaw, which is fused with the ventral margin of the skull (iv) The orbit or auditory capsules for lodging the ears (ii) The nasal or olfactory capsules containing the organs of smell (i) The brain case or tranium for enclosing the brain ![]()
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