The lateral processes of the first two vertebrae are developed from the ossification of the mesenchyme. 2. The centra of the second and third vertebrae are fused together forming a composite structure. 3. The "transverse processes" of the fourth vertebrae are homologous with the pleural ribs. 4. The ossa suspensoria are developed from the lateral and ventromesial processes from the basiventrals and form a kind of arch over the dorsal aorta. 5. The dorsal cartilaginous mass arching over the anterior vertebrae is formed by the basidorsals of the second, third, and fourth vertebrae. 6. The "perineural cartilage" serves to protect the spinal cord in the absence of the true neural arch of the first vertebra. 7. The claustrum is formed by the mesenchymatous rudiments which are intercalated structures. The claustrum rudiments ossify and get associated with some cartilaginous structures comparable to the supradorsals of the first vertebra. 8. The scaphium originates by the fusion of basidorsals of the first vertebra with the independent mesenchymatous tissue choncha stapedis. 9. The intercalarium is formed by the fusion of the basidorsals of the second vertebra and interossicular ligament. 10. The tripus is of complex origin and is formed by the basiventrals of the third vertebra, an independent mesenchymatous rudiment and a small ossification of the interossicular ligament.
