As the cavalry struggles wound down the infantry masses trundled forward.
The Ptolemaics got the initiative at the crucial point and launched their line forward except that several units failed to charge

3 units failed to charge and a potential disaster was facing Ptolemy as the initiative passed to the other side who experienced a similar failure with 2 of their units.
There then followed a scampering of leaders as they attached themselves to reluctant units and eventually everyone who could get in was in.
From a rules perspective I was initially a bit concerned but within another turn all was as I envisaged which was a more staggered set of fights rather than one long solid mass.