T.S. Eliot employs end rhyme, which refers to when the words at the ends of lines rhyme with one another. For example, in the first grouping of lines, the words at the ends of lines 1-2, I and sky, rhyme. Then, the words at the ends of lines 4-5, street and retreats, rhyme. Likewise, hotels and shells, the words at the ends of lines 6-7 rhyme. The words argument and intent rhyme, at the ends of lines 8-9. Finally, it and visit, the words at the ends of lines 11-12, rhyme. In other words, then, every line in the first group of twelve lines rhymes with another line except for line 3, "Like a patient etherized upon a table," and line 10, "To lead you to an overwhelming question." This makes these two lines stand out. Eliot sort of trains our ears to expect the end rhyme, and so when these lines fail to rhyme with others, it makes them conspicuous. It seems likely, then, that Eliot is drawing our attention to these lines, and so we ought to ask ourselves why he does that.
In the first of the non-rhyming lines, the speaker compares the evening sky to "a patient etherized upon a table": hardly a positive image. It implies a haziness, a confused muddle, even a lack of consciousness and control. It certainly sets the scene and begins to establish the disillusioned mood of the poem. The second of these lines describes "an overwhelming question" to which one is led after following streets that have some "insidious intent." The ellipsis at the end of the line implies that we may yet find out what that question is. It seems as though these lines are sort of left hanging as a result of their lack of end rhyme, and this draws our attention to them and their meanings and implications.