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 surgery and anaesthesia were uneventful , but 3 days after surgery , the patient reported an area of hypoaesthesia over L3 - L4 dermatomes of the leg which had been operated on ( loss of pinprick sensation ) without reduction in muscular strength .
### Output Text:
The surgery and anaesthesia were uneventful , but 3 days after surgery , the patient reported an area of hypoaesthesia over L3 - L4 dermatomes of the leg which had been operated on ( loss of pinprick sensation ) without reduction in muscular strength . 