Digestive Tract of Elasmobranchs in General — Continued page 



Pharynx 131 



Oesophagus 134 



Stomach 135 



Duodenum or middle intestine 136 



Liver 137 



Pancreas 138 



Spleen 138 



Valvular intestine 139 



Colon and rectum 141 



Cloaca 141 



Abdominal pores 142 



Bibliography 143 



VI. RESPIRATORY TRACT 



Respiratory Tract of Heptanchus maculatus 147 



Gill pouch or pocket 147 



Spiracle 147 



Gill or holobranch 148 



Gill supports 148 



Gill filaments 149 



Respiratory Tract of Elasmobranchs in General 150 



Gill pouch or pocket • 150 



Production of respiratory current 155 



Direction of respiratory current 156 



Circulation of blood in filaments 157 



Respiration or the exchange of gases 157 



Bibliography 158 



VII. CIRCULATORY SYSTEM 



Circulatory System of Heptanchus maculatus 160 



Arteries 161 



Ventral aorta 161 



Afferent arteries of the adult 161 



Efferent-collectors 161 



Branches of the efferent-collectors 162 



Hypobranchial arteries 162 



Efferent arteries 165 



Dorsal aorta 165 



Arterial supply to digestive tract 166 



Coeliac axis and its brancries 166 



Superior (anterior) mesenteric and its branches 167 



Inferior (posterior) mesenteric artery 167 



Arterial supply to extremities 168 



Arterial supply to deeper structures 169 



Caudal aorta 169 



Circulatory System of Elasmobranchs in General 170 



Heart 170 



Arteries 172 



Ventral or ascending aorta 172 



Afferent arteries of adult 172 



Capillaries 173 



Efferent-collectors 173 



Branches of efferent-collectors 178 



Hypobranchial arteries 178 



Arterial supply to head 180 



Efferent arteries 182 



[ix] 



