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Bashford Dean Memorial Volume 



Text-figure 71- 

 The joint process on the front margin on the antero-dorso'lateral plate; A, from outside; B, from front; 



C, from inside. 



a-h, axis of condyle; eg, condyle; psg, processus sub-glenoidalis; rg, supporting ridge for condyle; uj/, upper joint fossa. 



where this part is developed as a process, we may call this ''processus sub-glenoidalis" 

 (Jaekel). 



The condylus glenoidalis fits perfectly into the fossa glenoidalis, so that the plate 

 EB (and also the whole head) can easily be moved around the long axis of the condyle 

 (a-h). The previously mentioned processes round the fossa glenoidalis (Text-figure 73) 

 serve to reduce this movement to a relatively small degree only. The upper joint process 

 (ujp), when the head is moved upward, fits into the upper joint fossa (ujf) and thus limits 

 the possibility of the upward movement. The processus glenoidalis (pg) with its plane 

 inner surface comes in contact with the surface of the processus sub-glenoidalis' (p5g). 

 When the head is moved, the processus glenoidalis slides on the surface of the processus 

 sub-glenoidalis. In a downward movement the processus glenoidalis comes in contact 

 with the underside of the condyle ridge, which thus limits the possibility of the move- 

 ment. This is also reduced by another factor. The upper, rounded part of AL overlaps 

 the margin of EB and partly that of PM. On both these plates we find distinct rounded 

 impressions (see Text-figures 12, 18 and 42). In case the head was moved downwards AL 

 fitted into this impression, and thus stopped the movement. In spite of these arrange- 

 ments, which strongly reduced the mobility of the head, its movement was comparatively 

 large — in Dinichthys between 25 and 35 degrees. 



Evidently in living fishes the fossa of the condyle and the surface of the processes 



