एवमुक्त्वाऽर्जुनः संख्ये रथोपस्थ उपाविशत्। विसृज्य सशरं चापं शोकसंविग्नमानसः ॥

evam uktvārjunaḥ saṅkhye rathopastha upāviśhat visṛijya sa-śharaṁ chāpaṁ śhoka-saṁvigna-mānasaḥ

Having thus spoken on the battle-field, Arjuna sank down on the seat of the chariot, casting away his bow and arrow, his mind overborne by grief.

In plain words: Sanjaya, the narrator, says that after speaking, Arjuna sat down in his chariot. Overwhelmed by grief, he threw away his bow and arrows.