THE NECTURUS 7 



paired vomers seen extending posteriorly and laterally 

 from the premaxillse. They are ventral bones but appear 

 on the side of the skull. A part of the trabeculae is re- 

 tained as cartilage along the side of the skull and may be 

 seen at the side of the anterior extensions of the parietals. 

 A large preorbital cartilage extends out between the vomer 

 and the palatoquadrate. The palatoquadrate cartilage ex- 

 tends out laterally from the ossified quadrate. 



The quadrate marks the articulation of the jaw with the 

 skull and supplies a landmark for the identification of some 

 of the bones. Posterior to the quadrate cartilage is an 

 ossification of the chondrocranium, the prootic, which is 

 partially covered by the parietal. 



The opisthotic forms the postero-lateral angle of the 

 skull. It is ventral to the parietal and the squamosal. 



Drawing 3. Make a drawing of the ventral side of the skull X 10. 



The premaxillse are the anterior elements with teeth. 

 The maxillse are entirely missing. A cartilaginous area 

 separates the vomers. The under part of the skull is 

 formed mostly by the large median parasphenoid. The 

 palato-pterygoids appear on the ventral side, extending 

 laterally and posteriorly. A small articulating portion of 

 the quadrate appears as the condyle. The squamosal is 

 a thin plate of bone that connects the quadrate and the 

 opisthotic. The prootic appears in the region between the 

 parasphenoid and the outer line of the skull. The circular 

 stapes with the columella fits over the fenestra vestibuli 

 which is in the cartilaginous capsule of the ear. 



By using a razor blade that has been nicked slightly, the 

 skull may be sawed in two to show the size of the brain 

 ease, the organization of the inner part, and the relation 

 of the brain to the brain case. 



Teeth are found on the premaxillge, vomers, palatines and 

 palato-pterygoids. 



