Читать книгу Blackwell's Five-Minute Veterinary Consult: Reptile and Amphibian - Javier G. Nevarez - Страница 22

Unlike mammals, the bone epiphyses do not close in chelonians, snakes, and crocodilians. Epiphyses close later in life in lizards. Reptiles have intervertebral bodies rather than disks. These intervertebral bodies are softer and form convexities in the anterior or posterior aspect to allow for additional flexibility and decreased pressure on the spinal cord. This arrangement allows reptiles the ability to tolerate and recover from spinal trauma better than mammals.

Reptile orders are classified based on the presence or absence of fenestrae in the temporal region of the skull. Anapsids lack temporal openings (chelonians). Diapsids have two openings in the temporal region behind the orbit, one superior (dorsal) and one inferior (tuataras and crocodilians). Squamates are modified diapsids, with lizards having only a dorsal opening while snakes have lost the upper temporal arch between the two openings. The quadrate bone articulates between the maxilla and mandible allowing increased movement of the skull, including the maxilla, a feature critical for some reptile species. Streptostyly is the ability of the quadrate bone to move back and forth in snakes due to their modified diapsid skull. Lizards and crocodilians have powerful snapping jaws due to the adductor muscles that arise from the temporal fossae and insert at right angles to open the jaw.

The vertebral column of reptiles can be divided into three sections: presacral (24 in lizards, 18 in chelonians, over 200 in snakes), sacral, and caudal. The atlas and axis are more rigidly connected than in mammals, so primary neck movement is between the single occipital condyle and the vertebral column. The number of cervical vertebrae varies across species, with crocodilians and varanids having nine, chelonians, tuataras, and most lizards eight, and chameleons three to five. There is no subarachnoid space but a subdural space between the leptomeninges and the dura mater is present.