Choose the correct one.

Options

A. Optic nerve is the shortest
B. In amniotes the last cranial nerve is spinal accessory
C. In non-aminotes the last cranial nerver is vagus
D. Olfactory nerves have mixed fibres.

Answer

To solve the question "Choose the correct one," we need to evaluate each of the provided options regarding cranial nerves in reptiles and other vertebrates. Let's analyze each option step by step.

### Step-by-Step Solution:

1. **Option 1: "Optic nerve is the shortest."**
- The optic nerve is not the shortest cranial nerve. The shortest cranial nerve is actually the trochlear nerve, which is responsible for eye movement.
- **Conclusion**: This option is incorrect.

2. **Option 2: "In amniotes, the last cranial nerve is spinal accessory."**
- In amniotes (which include reptiles, birds, and mammals), there are 12 pairs of cranial nerves. The last cranial nerve in amniotes is the hypoglossal nerve, not the spinal accessory.
- **Conclusion**: This option is incorrect.

3. **Option 3: "In non-amniotes, the last cranial nerve is vagus."**
- Non-amniotes (lower vertebrates) have 10 pairs of cranial nerves, and the last cranial nerve in non-amniotes is indeed the vagus nerve.
- **Conclusion**: This option is correct.

4. **Option 4: "Olfactory nerves have mixed fibers."**
- The olfactory nerves are primarily sensory and are responsible for the sense of smell. They do not have mixed fibers (sensory and motor); they are purely sensory.
- **Conclusion**: This option is incorrect.

### Final Conclusion:
Based on the analysis of all the options, the correct answer is **Option 3: "In non-amniotes, the last cranial nerve is vagus."**

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