Struct that apparently defines no instances in Unix v6

I'm going through the code of Unix version 6 with the Lion's book. One of the header files (param.h, can be accessed here) defines the following structs:

/*struct to access integers*/

/*single integer */
struct { int integ; };

/*in bytes*/
struct { char lobyte; char hibyte; };

These structures don't seem to define any instance, nor are they named so they can be used later. Does anybody know what is their use?

Thanks