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Can you please check this passage and suggest whether past tense should be used here?

Figure 2. The scheme presents a part of the targeted wire guided thoracostomy explained in four steps (letter from a to d) with emphasis on the relation of the CCS dilatator and the guide wire. Each small picture represents cross-section of the whole thoracic cavity divided into frontal and back portion, and left and right side (only two dimensions of thoracic cavity are presented). In this scheme targeted position of the tip of the guide wire was/is back-left.
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Descriptions of figures or illustrations are almost always in present tense.
The exception would be if there has been a change from a previous version, and you are describing a former condition as contrasted with a current condition. Example: The illustration shows the statues as they were before they were destroyed in 2001. The massive figures were carved of sandstone, inscribed with writings at the base...
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Thanks AlpheccaStars.
Is 'portion' appropriate here?
Can I change 'frontal' to 'front'?