[3] Forbes lectured on comparative anatomy at Charing Cross Hospital Medical School.

As an anatomist, he wrote valuable papers on the muscular structure and voice organs of birds.

On 8 February 1878, Forbes was elected Secretary of the Cambridge Natural History Society.

In 1880 Forbes visited the forests of Pernambuco, Brazil, and published an account of his trip in The Ibis in 1881.

In 1882 he travelled to west Africa to study the native fauna, starting from the mouth of the Niger delta (an area where British merchants had set up large scales of trade, it would become part of the Niger Coast Protectorate or the Oil Rivers Protectorate in about two year).