Edit in JSFiddle

var myModel = Backbone.Model.extend({
    initialize:function(a,b,number){console.log(a,b,number)}, //log paramaters
new myModel({a:'a'},{b:'b'},1); //passing attributes, options, and random paramater

/* Note: Specifically in this example where a model is being extended and instantiated the first argument passed is used by the consturctor to populate the model with data, the second argument is the options object, after these arguments any additional arguments passed will also be passed to the initialize function (e.g. 1). */