58 



it Einiim()li)j;y and Zoology 



A true squamosal bone is sometimes considered not to exist 

 among Amphibia, and the so-called squamosal bone is considered 

 to be rather an investing bone on the surface of the quadrate, and 

 for this reason is sometimes called the jiaraquadrate. 



The quadrate (8) is an irregularly shaped little bone with 

 somewhat the appt-araiice when in position, of a wedge between the 

 ptergoid and the squamosal. Functionally it serves as a piece in- 

 terposed between the skull and the mandible, and forming an 

 articular surface for the latter. The knob-like anterior ventral 

 end of the quadrate consists of an articular process, fitted with 

 a socket to receive the rounded knob ( articulare) of the mandilile. 



The ptergoid (7) is a spade-shaped bone which projects down- 

 ward from the ventral side of the skull. It articulates with the 

 main body of the skull by means of a hollow, rounded process which 

 articulates down over a knoij-iike projection on the occijiital bone. 

 Aside from the articulation with the occipital, the ptergoid articu- 

 lates posteriorally with the (luadrate and the squamosal. 



The squamo-palatines (1:1) are long rather slender bones, flat- 

 tened anteriorally. At about one-third of their length, from the 



anterior end, they articulate dorsally with the parasphenoid and 

 project down onto that bone for the remainder of their length. 

 These projections are provided with teeth along the median line. 

 Anteriorally the squamo-palatines articulate with the premaxillary 

 and the maxillaries. 



The parasphenoid (11) is the flattest and most extensive bone 

 in the skull, and forms nearly the whole floor of the brain case, and 

 at the same time the roof of the mouth. It is nearly the shape of 

 a parallelogram with rounded corners, but it is a little broader in 

 the optic region and becomes somewhat narrowed anteriorally. It 



