You can search for an itenary on RATP website or through there mobile application called "Bonjour RATP": ( Android | iOS)
Bus
Line 21: Gare Saint-Lazare / Porte de Gentilly – Stop : Daviel
Line 38: Porte d'Orléans / Gare du Nord. Stop : Denfert-Rochereau
Line 68: Châtillon-Montrouge Métro / Place de Clichy Métro. Stop : Denfert-Rochereau
Line Orlybus: Aérogare d'Orly Sud / Denfert-Rochereau. Stop : Dareau-Saint-Jacques
Line 216 : Denfert- Rochereau/Metro/Rer . Stop : Dareau – Saint -Jacques
Metro
Line 6: Nation / Charles de Gaulle-Etoile. Stop: Glacière. Take street called Rue de la Santé. Turn right, street Rue Cabanis
RER
Line B: Stop: Denfert-Rochereau
Plane
From Orly Airport: Take Orlybus until Denfert-Rochereau, then metro line 6 toward Nation. Stop at Glacière then get back to Boulevard Saint-Jacques until street called Rue de la Santé.
From Orly's Airport (choice 2)Take Orlyval until Anthony, RER B toward Roissy-Charles de Gaulle/Mitry-Claye. Stop at Denfert-Rochereau and take metro line 6, toward Nation. Stop at Glacière and take by feet the Boulevard Saint-Jacques until the street called Rue de la Santé.
From Roissy-Charles de Gaulle Airport: Take RER B, toward Robinson/St-Rémylès-Chevreuses. Stop at Denfert-Rochereau and take metro line 6, toward Nation. Stop at Glacière and take by feet the Boulevard Saint-Jacques until the street called Rue de la Santé.