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: MRI demonstrated hyperintense T2 signals in the cervical cord and right brachial plexus roots indicative of both myelitis and right brachial plexitis .
### Output Text:
MRI demonstrated hyperintense T2 signals in the cervical cord and right brachial plexus roots indicative of both myelitis and right brachial plexitis . 