Beyond the lower rungs of the totem pole… 

First of all, investment banking represents a pyramid structure whereby there are a ton of analysts and very few MDs. Despite the difficulty and intense competition to land an analyst investment banking gig, there are about 1,000 investment analysts hired per year, at bulge bracket banks and top boutiques. A typical BB bank for example, has about 100 analysts ever year. An average associate class is about 50 per year with some banks like JP Morgan having around 60 and some banks like Morgan Stanley having around 30. Basically, as you go up in the pyramid, there are less and less high-profile bankers with less VPs than Associates, less Directors / EDs than VPs and very few MDs at the top.

At the VP and Director / Executive Director level, you really can't get hired from the outside as all the hires are lateral hires. VP and Director-level hires originate from other investment banks. At the MD-level, most hires come from lateral hires from other investment banks as well though there are some "client management" hires from high-level industry professionals. But generally, if you want to get into higher echelon investment banking, you need to enter as an associate since the other pathways aren't as etablished. Analyst and associate hires are the only two direct ways to getting hired into investment banking - nonetheless, analysts typically follow a two (maybe three) year and out model.