Page:An Introduction to the Study of Fishes.djvu/114

86 2. Mesencephalic arch, composed of basisphenoid, alisphenoid, parietal, and mastoid.

3. Prosencephalic arch, composed of presphenoid, orbitosphenoid, 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, aud coracoid; its appendage consists of the ulna, radius and carpal.

2. Hyoid or stylo-hyoid arch, composed of stylo-hyal, epihyal, ceratohyal, basihyal, glossohyal, and urohyal; its appendage is the branchiostegals.

3. Mandibular or tympano-mandibidar arch, composed of epi-, meso-, pre-, and hypo-tympanic, and the bones of the lower jaw; its appendage consists of the præoperculum and the other opercles.

4. Maxillary or palato-maxillary arch, composed of palatine, maxillary, and premaxillary; its appendage consists of the pterygoid and entopterygoid.

Parts of the splanchnoskeleton are held to be the ear-capsule or petrosal and the otolite, the eye-capsule or sclerotic, the nose-capsule or "ethmoid" and turbinal; the branchial arches.

The bones of the dermoskeleton are the supratemporals, supraorbitals, suborbitals, and labials.

B. In the second method of classifying the bones of the skull prominence is given to the facts of their different origin as ascertained by a study of their development. The parts developed from the primordial skull, or the cartilaginous case protecting the nervous centre are distinguished from those which enclose and support the commencement of the alimentary canal and the respiratory apparatus, and which, consisting of several arches, are comprised under the common name of