Hi Ricardo,
Your doubt is "well founded" The 1300 Series comes in two versions. One with Integrated Antennas and one with RP-TNC type connectors for external antennas. Neither model has both Internal and External Antennas;
The Cisco Aironet 1300 Series with integrated antenna can be quickly installed to provide a LAN bridge to a remote site or multiple sites. The 1300 Series with antenna connectors supports a variety of Cisco 2.4-GHz antennas, providing range and coverage versatility.
Antenna Interface
AIR-BR1310G-x-K9 or AIR-LAP1310G-x-K9:
Air interface (integrated directional antenna)
AIR-BR1310G-x-K9-R or AIR-LAP1310G-x-K9R:
Two RP-TNC type connectors for external antennas
From this good doc;
http://www.cisco.com/en/US/products/ps5861/products_data_sheet09186a00802252e1.html
Hope this helps!
Rob