In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The inferior colliculus ( IC ) is primarily involved in the processing of auditory information , but it is distinguished from other auditory nuclei in the brainstem by its connections with structures of the motor system .
### Output Text:
The inferior colliculus ( IC ) is primarily involved in the processing of auditory information , but it is distinguished from other auditory nuclei in the brainstem by its connections with structures of the motor system . 