30 THE SALAMANDER 



squamosal extends from the quadrato-mandibular joint along the 

 processus oticus of the palato-quadrate and becomes more or less fused 

 with the periotic bone above the horizontal canal. While there is a 

 distinct tendency for the bone to be 'T'-shaped it is not so definite as 

 in the Frog. 



A quadrato-jugal has been described by Stadtmiiller. According 

 to him it appears first in a larva of about 27 mm. and always remains 

 small. In the adult it fuses homocontinuously with the ossified por- 

 tion of the quadrate, from which it becomes indistinguishable. 



The investing bones of the ventral surface are the parasphenoid, 

 the pre-vomers, and the pterygoids. 



'Th.Q parasphenoid {sphenoid^ Duges; Kei/hin, ¥loffm3.nn; vomer ^m 

 part, Broom; vomer -^ pterygoids^ Kesteven). This bone is the largest 

 in the skull and is characteristic of Amphibia. It forms at one and 

 the same time a bony floor to the cavum cranii and a roof to the 

 mouth, and is the only median bone in the skull. Posteriorly it 

 extends for some distance under the ear capsules on either side, but 

 hardly so far, comparatively, as in the Frog. In the orbital region 

 the edges turn upwards to meet the orbito-sphenoid, so that the 

 bone becomes gutter-shaped in cross-section. The internal carotid 

 artery passes into the cranial cavity through a canal — the carotid canal 

 (can. car.) — between the parasphenoid and the otic capsule. 



Until quite recent years the parasphenoid has been looked upon 

 as a typically amphibian bone, which was also present in Reptiles, 

 but in a very reduced state. Recently, however, Broom has sought 

 to identify the anterior part of the amphibian, and the whole of the 

 reptilian, parasphenoid with the mammalian vomer., while Kesteven 

 (19 1 6 and 1926) claims that the posterior part of the amphibian 

 parasphenoid is represented in Reptiles and Mammals by the ptery- 

 goids. Both these authors base their views mainly upon palaeonto- 

 logical evidence. 



The pre-vomers (o.p-v.) (Broom) are perhaps better known as the 

 vomero-palatines, but, if one accepts the above-mentioned conclusions 

 with regard to the homology of the mammalian vomer, the bones 

 now to be described can be none other than the pre-vomers. Whether 

 any palatine element is represented will be considered later. The 

 paired pre-vomers form a bony floor to the nasal capsules. Each bone 

 articulates with the pre-maxilla and maxilla laterally, while mesially 

 its anterior border bounds the large internasal space, behind which 

 it is approximated to its fellow on the other side for a short distance. 

 The edge of the bone then diverges from the middle line and follows 

 the curve of the dentigerous portion. The bone also surrounds the 



