Charak Samhita
कियन्तःशिरसीयश्च त्रिशोफाष्टोदरादिकौ। रोगाध्यायो महांश्चैव रोगाध्यायचतुष्टयम् ॥४०॥
17. Enumeration of diseases relating to the head; 18. Three types of swelling; 19. Eight abdominal diseases; 20. The major chapter on the enumeration of diseases; The above mentioned four chapters constitute the tetrad on diseases.
english translation
kiyantaHzirasIyazca trizophASTodarAdikau। rogAdhyAyo mahAMzcaiva rogAdhyAyacatuSTayam ॥40॥
hk transliteration by Sanscript