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: Right carotid angiograms failed to show the SSS and inferior sagittal sinus , suggestive of venous sinus thrombosis .
### Output Text:
Right carotid angiograms failed to show the SSS and inferior sagittal sinus , suggestive of venous sinus thrombosis . 