The cranial capacity was highest among the:

Options

A. Cro-Magnon Man
B. Neanderthal Man
C. Java Man
D. Peking Man.

Explanation

To determine which group had the highest cranial capacity among the given options, we can analyze the cranial capacities of each group mentioned:

1. **Pro-Medulline Men**: This group is not well-defined in terms of cranial capacity, but it is generally considered to have a cranial capacity that is less than that of Neanderthals.

2. **Neanderthal Men**: Neanderthals had an average cranial capacity of approximately 1600 cm³. This is larger than the average cranial capacity of modern humans, which is around 1400 cm³.

3. **Java Men**: Java Man, which is an early human ancestor (Homo erectus), had a cranial capacity ranging from about 900 cm³ to 1100 cm³, which is significantly lower than that of Neanderthals.

4. **Peking Men**: Peking Man, also a Homo erectus, had a cranial capacity similar to Java Man, around 1000 cm³ to 1100 cm³.

Based on the cranial capacities analyzed:

- Pro-Medulline Men: Not defined, likely lower than Neanderthals.
- Neanderthal Men: 1600 cm³ (highest).
- Java Men: 900-1100 cm³ (lower).
- Peking Men: 1000-1100 cm³ (lower).

Thus, the group with the highest cranial capacity is **Neanderthal Men**.

### Final Answer:
**B) Neanderthal Men**