Public IP address

I would llike to know why I was assigned to a Public address from comcast beginning with 73.x.x.x to my modem but when I do a trace route from my machine to google.com, my next hop route from my machine

begins with 96.x.x.x.  I would think my next hop from my private address would be 73.x.x.x but it does not show 73.x at all. it shows that my next hop is 96.x.x.x.  I looked in my my router and modem and it specifies that the the gateway is 73.x.x.x.   I understand that the the wan port gets nat from my private IP 192.x.x.x to a public 73.x.x.x and the gateway is also on the same network of 73.x.x.1 but that gateway 73.x.x.1 should be on your boundary network device but the trace route doesnt show that.  it shows 96.x.x.x.  So is the 73.x.x.x masked? or please explain

Thanks