Cortina was an early 1970's, boom era brand that appears to have been contract manufactured in Italy, as there was actually a Cortina Bicycle Company in the US, at a time when foreign manufactuers rarely had US offices. There were at least 3 models that used the Valentino Extra derailleurs. However, yours appears to be a Racer (yes, that is the actual model name) which sold for $125 US in 1973. During this period the brand appeared quite attractive to many novice cyclists, as Atala or Bottecchia models with Valentino Extra derailleurs and aluminum rims typically cost $40 more. However, the Cortina usually cut costs on other components, which customers did not pay as much attention to. The brand is relatively rare, though I wouldn't consider it collectible.