THE SKELETON 33 



prominent posterior mental -process. The anterior two-thirds of each 

 ramus bears a single row of functional teeth, mesial to which a row 

 of reserve teeth can be demonstrated in transverse sections. (For 

 details of the teeth, see p. 262.) 



The structure of the mandible, in both the larva and adult, has 

 been thoroughly investigated by Gaupp (191 1) and Stadtmuller 

 (1924). Both accounts are in agreement and correct that of Parker 

 (1882) by showing that the j-/>/^;?zW (Operculare of the German 

 authors) is present in the larva only, and is resorbed entirely in the 

 adult. There are therefore two investing bones only in the lower jaw, 

 namely, a dentary and a pre-artkular (Goniale), while two replacing 

 ossifications also occur in the persisting Meckel's cartilage, viz. 

 the articular at the proximal end and the mento-Meckelian at the 

 symphysis. 



Meckel's cartilage (c.M.) persists as the primary skeleton of the 

 lower jaw throughout life, and is unossified in the major part. It 

 remains exposed at the proximal end between the two investing bones 

 — dentary and pre-articular, while the anterior end tapers to a point 

 and terminates a short distance from the middle line, its mesial ex- 

 tremity having become ossified as a mento-Meckelian (Mento-mandi- 

 bulare, Stadtmuller), so that the median symphysis is solid bone. 

 This ossification occurs quite late, well after metamorphosis, and 

 becomes fused homocontinuously with the dentary, which is probably 

 the reason that lead W. K. Parker to say (p. 177) 'the Salamander 

 has no mento-Meckelian bone'. The extreme proximal end of Mec- 

 kel's cartilage is the only element of the lower jaw to come into 

 contact with the suspensorium. Of this the actual surface remains 

 cartilaginous, but the deeper portions become transformed into a 

 small bony knob, the articular (o.art.). According to Stadtmuller 

 this ossification also occurs very late and is first discernible in a 

 metamorphosed individual of about 43 mm. long. 



Investing Bones. The dentary (o.den.) forms the principal ele- 

 ment of the adult mandible. It covers almost the whole of Meckel's 

 cartilage laterally and most of its dorsal and ventral surfaces, and 

 bears teeth (see p. 263). In transverse section it is more or less C- 

 shaped, with the opening of the *C' towards the mesial side. Anteriorly 

 it forms an almost complete circle around Meckel's cartilage, but it 

 opens out posteriorly and tapers at the same time, so that it terminates 

 a little anterior to the articulation as a thin lath on the lateral aspect 

 of Meckel's cartilage. Its fusion with the mento-Meckelian has 

 already been mentioned. W. K. Parker describes its dorso-mesial 

 portion as a separate element, the splenial^ but according to 



4038 n 



