Puer os aperit, et medica dentes eius spectat.

Latin has no articles, so there is no separate word for the or a/an.

So:

• puer can mean the boy or a boy
• medica can mean the female doctor or a female doctor

Context tells you which is natural in English.

Latin often omits a possessive when it is obvious, especially with body parts or very close personal belongings.

So puer os aperit literally says the boy opens [the] mouth, but the natural sense is the boy opens his mouth.

If Latin wanted to make the possession explicit, it could do so, but here it is unnecessary.

Puer is nominative singular. It is the subject of aperit, the one doing the action.

Dictionary form:

• puer, pueri = boy

This is a second-declension masculine noun, one of the -er nouns.

The -t ending means third person singular in the present tense:

• aperit = he opens / she opens / it opens
• spectat = he looks at / she looks at / it looks at

Because the subjects are singular:

• puer → singular
• medica → singular

the verbs are singular too.

Here os is accusative singular, because it is the direct object of aperit.

The tricky part is that os is a neuter noun, and in Latin neuter nominative and accusative are always the same in form.

So:

• nominative singular: os
• accusative singular: os

That is why the form does not change.

This noun is:

• os, oris = mouth

Yes, here it means mouth.

Latin actually has two different nouns spelled os in the nominative singular:

• os, oris = mouth
• os, ossis = bone

They are different words with different genitives. In this sentence, the context makes mouth the only sensible meaning: the boy opens his mouth.

Medica is the feminine nominative singular form, so it means a female doctor or woman doctor.

• medicus = male doctor
• medica = female doctor

Here it is being used as a noun, even though historically it is related to an adjective. Latin often does that.

• dentes is accusative plural
• eius is genitive singular

Why?

dentes

It is the direct object of spectat:

• the doctor looks at / examines the teeth

Dictionary form:

• dens, dentis = tooth

So:

• nominative singular: dens
• accusative plural: dentes

eius

This means his / her / its or more literally of him / of her / of it. It is in the genitive, because it shows possession:

• dentes eius = his teeth

This is a very important Latin point.

Suus, sua, suum refers back to the subject of its own clause.

In the second clause, the subject is medica. So:

• medica dentes suos spectat would mean the doctor examines her own teeth

But that is not what is meant. The teeth belong to the boy, not to the doctor. So Latin uses:

• eius = his / her, referring to someone other than the subject of this clause

That is why eius is correct here.

Its basic meaning is looks at, watches, or observes.

But in context, especially with a doctor and teeth, English naturally says examines. So:

• spectat literally: looks at
• natural English here: examines

This is very common in translation: the Latin word may be simpler than the most natural English wording.

The word order here is fairly straightforward, but Latin word order is generally more flexible than English word order because the endings show what each word is doing.

This sentence is:

• Puer os aperit
• et medica dentes eius spectat

That is roughly:

• subject – object – verb
• and subject – object – possessive – verb

Latin often likes to put the verb near the end, as it does here, but it does not have to.

Because the cases already show the grammar, Latin can move words around for emphasis more easily than English can.