The Optic capsules.
The skeletal structures developed in connection with the optic capsule do not become united to the skull. They consist of:—
(a) the sclerotic, a cartilaginous sheath investing the eye and bearing
(b) a ring of ten small bony scales.
There is no lachrymal bone.
The Olfactory or Nasal capsules.
The basicranial axis in front of the basisphenoid remains cartilaginous, neither presphenoid nor mesethmoid bones are developed, and the orbits in a dry skull communicate by a wide space through which the second, third, fourth, and sixth cranial nerves pass out. Separate nasal bones also do not occur, the large prefrontals extending over the area usually occupied by both nasals and lachrymals.
The only bone developed in connection with the nasal capsules is the vomer (fig. 39, 19), an unpaired bone lying ventral to the mesethmoid cartilage, and in contact laterally with the maxillae, premaxillae and palatines.
3. The Upper Jaw and suspensorial apparatus.
A number of pairs of bones are developed in connection with the upper jaw and suspensorial apparatus, one pair, the quadrates, being cartilage bones, while the rest are all membrane bones.