The bones of the fish-skull are, according to him, primarily divisible into those of the neuroskeleton, splanchnoskeleton, and dermoskeleton.
The bones of the neuro- or proper endoskeleton are arranged in a series of four horizontally succeeding segments: the occipital, parietal, frontal, and nasal vertebræ; each segment consisting of an upper (neural) and a lower (hæmal) arch, with a common centre, and with diverging appendages.
The neural arches of the four vertebræ, in their succession from the occiput towards the snout, are:—
1. Epencephalic arch, composed of the occipitals.
2. Mesencephalic arch, composed of basisphenoid, alisphenoid, parietal, and mastoid.
3. Prosencephalic arch, composed of presphenoid, orbito-sphenoid, frontal, and postfrontal.
4. Rhinencephalic arch, composed of vomer, prefrontal, and nasal.
The hæmal arches in the same order of succession are:—
1. Scapular or scapulo-coracoid arch, composed of suprascapula, scapula, and coracoid; its appendage consists of the ulna, radius and carpal.
2. Hyoid or stylo-hyoid arch, composed of stylohyal, epihyal, ceratohyal, basihyal, glossohyal, and urohyal; its appendage is the branchiostegals.