Discipula dicit se duodeviginti versus in commentario scripsisse.

This sentence has:

• a main clause: Discipula dicit = The schoolgirl says
• an indirect statement: se duodeviginti versus in commentario scripsisse = that she wrote eighteen lines in the notebook/commentary

Latin often uses the accusative + infinitive construction for indirect statement after verbs of saying, thinking, knowing, hearing, and so on.

So instead of something more English-like such as that she wrote, Latin says:

• se = the subject of the indirect statement, put in the accusative
• scripsisse = the verb of the indirect statement, put in the infinitive

That pattern is extremely common in Latin.

Because se is the reflexive pronoun. It points back to the subject of the main verb, here discipula.

So:

• Discipula dicit se ... scripsisse = The schoolgirl says that she herself wrote ...

If Latin used ea, that would usually mean she in a non-reflexive sense, often referring to some other female already mentioned, not back to the subject of dicit.

So se tells you that the writer and the speaker in the sentence are the same person.

Because in an indirect statement, the subject of the infinitive is put in the accusative case.

In English, we say:

• She says that she wrote

In Latin, the equivalent structure is more like:

• She says herself to have written

That sounds unnatural in English, but it shows the Latin grammar more clearly:

• se = accusative subject of scripsisse
• scripsisse = infinitive

So se is not the direct object of dicit. It is the subject of the infinitive inside the indirect statement.

Scripsisse is the perfect active infinitive of scribo, scribere, scripsi, scriptum = to write.

It is built from the perfect stem:

• scrips-
  • -isse = scripsisse

In indirect statement, the tense of the infinitive shows time relative to the main verb, not absolute time by itself.

So here:

• dicit = she says (present)
• scripsisse = to have written

This means the writing happened before the saying.

So the sense is:

• She says that she wrote
• more literally, She says that she has written / had written, depending on context

Because after dicit Latin normally uses an indirect statement, not a clause introduced by that with a finite verb.

English:

• She says that she wrote eighteen lines

Latin:

• Discipula dicit se ... scripsisse

So after dicit, Latin does not usually say something like quod scripsit here. Instead it uses:

• accusative subject: se
• infinitive verb: scripsisse

This is one of the most important Latin sentence patterns to learn.

Here versus is accusative plural, meaning lines.

The noun is versus, -us (masculine, 4th declension), meaning line of verse or simply line in this kind of context.

Its accusative plural is also versus.

That can be confusing, because the form looks like some other singular forms in Latin. But here it must be plural because of duodeviginti = eighteen.

So:

• duodeviginti versus = eighteen lines

And versus is accusative because it is the direct object of scripsisse.

Duodeviginti means eighteen.

It is formed in a subtractive way:

• duo de viginti = literally two from twenty

So it means 20 - 2 = 18.

This is a normal Latin way to form some numbers. Another common example is:

• undeviginti = nineteen, literally one from twenty

Also, duodeviginti is indeclinable, so it does not change its form for case, gender, or number.

Because in with the ablative means in or on in the sense of location.

Here commentario is ablative singular of commentarius.

So:

• in commentario = in the notebook / in the commentary / in the exercise book, depending on context

Compare:

• in + ablative = location, in/on
• in + accusative = motion toward, into

So:

• in commentario scripsisse = to have written in the notebook
• but in commentarium scribere would suggest to write into the notebook

Commentarius can mean several related things, depending on context:

• notebook
• exercise book
• written commentary
• record
• journal

In a school context, many learners will understand in commentario as something like:

• in her notebook
• in her exercise book

So the exact English word may vary, but the Latin grammar stays the same.

The word order is fairly natural Latin, but Latin is much more flexible than English.

The sentence is:

• Discipula — subject
• dicit — main verb
• se ... scripsisse — indirect statement
• duodeviginti versus — object of the infinitive
• in commentario — prepositional phrase

Latin often places the verb of saying early and then gives the indirect statement after it. That is what happens here.

You could rearrange parts without changing the core meaning, for example:

• Discipula se duodeviginti versus in commentario scripsisse dicit

That still means the same thing. The original order is simply clear and idiomatic.

A direct version would be something like:

• Discipula dicit: duodeviginti versus in commentario scripsi.

That means:

• The schoolgirl says: I wrote eighteen lines in the notebook.

Notice the changes:

• se disappears, because in direct speech the speaker says I
• scripsisse becomes scripsi, a finite verb
• the person shifts from third person in the main sentence to first person in the quoted speech

So the indirect statement is a way of reporting that same content without quoting the speaker directly.