CHAPTER IV. The Evidence of the Respiratory Apparatus

THE EVIDENCE OF THE RESPIRATORY APPARATUS

Branchiæ considered as internal branchial appendages--Innervation of branchial segments--Cranial region older than spinal--Three-root system of cranial nerves: dorsal, lateral, ventral--Explanation of van Wijhe's segments--Lateral mixed root is appendage-nerve of invertebrate--The branchial chamber of Ammocoetes--The branchial unit, not a pouch but an appendage--The origin of the branchial musculature--The branchial circulation--The branchial heart of the vertebrate--Not homologous with the systemic heart of the arthropod-- Its formation from two longitudinal venous sinuses--Summary 148