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: There were no significant differences between groups in the mean diameters of the intradural internal carotid , sphenoidal segment of the middle cerebral , precommunicating segment of the anterior cerebral , or basilar arteries ( p greater than 0 . 05 for all comparisons , unpaired t - tests ) .
### Output Text:
There were no significant differences between groups in the mean diameters of the intradural internal carotid , sphenoidal segment of the middle cerebral , precommunicating segment of the anterior cerebral , or basilar arteries ( p greater than 0 . 05 for all comparisons , unpaired t - tests ) . 