136 



PEOr. OWEN ON THE HOMOLOGY 



the spiny Dogfish (AcantMas)it8 progress is there arrested. The 

 direction of the pineal tube is forward as well as upward in all fishes. 

 In that esculant form, Protopterus (fig. 2), the first-found member 

 of wbich was referred to the Amphibia under the name ^^Lepido- 

 siren,''^ the width and length of the " infundibulum " continued 

 from the flattened discoid body, 8, cut ofi'from the bucco-branchial 

 cavity, 9, lo, by a thin lamelliform extension of the basis cranii, is 

 continued by a proportionally wide "third ventricle" into the 

 base of a conical " conarium," 7, as large as the cerebellum itself, 

 from the apex of whicb conarium avascular membranous tubule is 

 continued upward and forward through a gristly part of the cra- 

 nium to the scalp*. 



The homology thus suggested of the conario-hypophysial tract 

 in Yertebrates with a vascular canal traversing a corresponding 

 part of the brain in Invertebrates (fig. 3, 7, lo), called for further 

 evidence ; and such has been amply yielded by Embryology. 



Fig. 4. 



Mammalian einhryo. — 1. Neural axis. 2. Vertebral axis. 3. Cerebellar 

 vesicle and medulla oblongata = epenceplialoii. 4. Optic vesicle=mesenee- 

 phalon. 5. Vesicle of third Tentricle. 6. Cerebral Tesicle = prosencephalon. 

 7. Pineal portion, 8. Pituitary or infundibular portion, of the conario-hypo- 

 physial tract. 9-10. Bucco-branchial cavity. 11. Stomach. 12. Small intes- 

 tine. 13. Large intestine. 14. Vent. 15. Heart and chief blood-vessels. 

 16. Primordial kidney. 17. Urinary bladder. 18. Pedicle of allantois. 

 19. Pedicle of umbilical vesicle. 20. Liver. 



* Tom. cit. p, 282, fig. 186. 



