[Grammar] the occupations of graveyard attendant and custodian of learning

[suprunp]

An ill-kept lawn ran down in front of them to a row of amputated railings, beyond which was College Road and the town cemetery, a conjunction responsible for some popular local jokes. Lecturers were fond of lauding to their students the comparative receptivity to facts of 'the Honours class over the road', while the parallel between the occupations of graveyard attendant and custodian of learning was one which often suggested itself to others besides the students.
(Kingsley Amis, LUCKY JIM)

Why are the articles (seemingly) left out?

the occupations of a graveyard attendant and (a) custodian of learning.

Thanks.

 

[Tdol]

Talking in general