While the majority of the surviving Original Manuscript is in the handwriting of Oliver Cowdery, the handwriting of two other scribes occurs on a few pages in the First Nephi portion. One of these additional scribes may be Reuben Hale. In addition, twenty-eight words in Alma 45 (first part) have been tentatively identified as Joseph Smith's handwriting (Skousen 1991:5) [Shirley R. Heater, "History of the Manuscripts of the Book of Mormon," in Recent Book of Mormon Developments, Vol. 2, p. 70]
According to Royal Skousen, in Alma 45:22 of the Original Manuscript, Oliver Cowdery suddenly stops acting as scribe and Joseph Smith himself takes over the scribe's task for twenty-eight words:
yea in every citty throughout all the land which was possessed by the people of Nephi and it came to pass that they did appoint priests and teachers
These twenty-eight words in Joseph Smith's hand are written very carefully. And except for one spelling variant (citty), all the extant words are spelled according to standard orthography.
One possible explanation for this momentary switch in scribes is that it represents Oliver Cowdery's unsuccessful attempt to translate. It even suggests that Oliver, like Peter the apostle walking on the water, succeeded at first. For instance, verse 5 of section 9 in the Doctrine and Covenants implies an initial success on Oliver's part:
And, behold, it is because that you did not continue as you commenced, when you began to translate, that I have taken away this privilege from you.
Nonetheless, there is, in my opinion, some difficulty with the suggestion that these twenty-eight words in Alma 45 represent Oliver Cowdery translating. One problem is that the switch to Joseph Smith's hand occurs in the middle of the narrative, in fact, in the middle of a sentence (although at a point of semiclosure). One would think that Oliver Cowdery's attempt to translate would have come at a more suitable break in the narrative.
My explanation for this scribal switch is that there was a sudden need for the scribe to break off and Joseph Smith had to get down what he was currently viewing in the interpreters, so he wrote it down himself. The reason Joseph would have had to do this is possibly explained by Emma Smith's claim in her 1879 interview with her son Joseph Smith III that his father, Joseph Smith Jr., started dictation sessions without prompting:
I am satisfied that no man could have dictated the writing of the manuscripts unless he was inspired; for, when acting as his scribe, your father would dictate to me hour after hour; and when returning after meals, or after interruptions, he would at once begin where he had left off, without either seeing the manuscript or having any portion of it read to him. This was a usual thing for him to do. It would have been improbable that a learned man could do this; and, for one so ignorant and unlearned as he was, it was simply impossible. (Joseph Smith III, "Last Testimony of Sister Emma," 290)
This ability to continue without prompting suggests that before ending a dictation session or going on to the next portion of text, Joseph Smith would have to finish getting copied down all of what he was viewing; otherwise the uncopied part would be lost. In other words, Joseph had to deal with what was in front of him and could not quit until what he was seeing was transcribed.
Joseph's careful handwriting for these twenty-eight words as well as his accurate spelling for several difficult words (throughout, possessed, appoint) suggests that he might have been visually copying and not listening to someone else dictating the text . . . if this explanation is right, then Joseph Smith was viewing at least these twenty-eight words . . . and this is evidence in the Original Manuscript for the minimal amount of text Joseph Smith had access to as he was dictating. [Royal Skousen, "Translating the Book of Mormon, Evidence from the Original Manuscript," in Book of Mormon Authorship Revisited, pp. 71-75]