Similar to outgoing link practice, Vertical cross link within web pages in your website is a good practice too, internal cross links are like quick short cut links, it allows readers to find other info web pages within your website quickly.
If there are lots of pages within a section, you can reference other web pages within the section though cross links in paragraphs, this is if there is a need to help the reader explore further on the term/subject that is covered in other web pages within the section that is related to this current web page, you do not need to repeat again the same content that is covered in other web page, just a handy quick cross link within the paragraph is good enough to help readers find the needed info.
Internal cross link is not limited to the web pages within same section, you can cross link to other web pages in other section as well. For example, your current page is about introduction to orange, within the paragraph you have mention other fruits like apple, and you do have another section that covers apple, you can create a quick cross link for the word apple to the apple section web page.
This practice was long recommended by professional webmasters and widely used by large content websites, but a lot of webmasters are just lazy to do this extra work, do note that search engines welcome this practice too. Again, do not overdoing it, only cross link when needed and there is no need to cross link to the same web page several times within the same web page, this is basically signaling search engines that you are trying to manipulate their results and might risk getting your web page drop out of the index.
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