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: In experimental animals excess deposition of collagen and glycoaminoglycans was observed in the subendothelial and medial layer of the aortic wall , together with prominent basal membrane substance around aortic smooth muscle cells .
### Output Text:
In experimental animals excess deposition of collagen and glycoaminoglycans was observed in the subendothelial and medial layer of the aortic wall , together with prominent basal membrane substance around aortic smooth muscle cells . 