HOMOLOGY. 



9 



free or peripheral end and maintaining its communication 

 with the " ventricle," from the floor of which the " infundi- 

 buliwn " extends to join the pituitary body. In Proiopterus 

 (fig. 2), the first-found member of which was referred to the 

 Amphibia under the name " Lepidosiren," and belongs to 

 the same'collective " Branchiate group" *, 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 which conarium a vascular membranous tubule is 

 continued upward and forward through a gristly part of the 

 cranium to the scalp f. 



The homology thus suggested of the conario-hypophysial 

 tract in Vertebrates with a vascular canal traversing a cor- 



Pig. 3. 



Larva of SpJiinx. — 1. jSTeural axis, 3. Hind brain. -5. Connecting 

 tracts or " crura," of 6, Fore brain. 7. jN'enral mouth, or neurostome. 

 7-10. Pharynx and gullet. 11. Stomach. 12. Hepatic intestine. 

 13. Rectum. 14. Vent. 15. Heart and chief blood-vessels. 



respondmg part of the brain in Invertebrates (fig. 3, 7, lo), 

 called for further evidence ; and such has been amply yielded 

 by Embryology. 



In the Vertebrate embryo (fig. 4) the myelencephalon, i-6, 

 first appears as a longitudinal channel of the epiblast, opening 

 " neurad and soon, by upward or neural extension and 

 * Anat. of Vert. vol. i. pp. 6, 7. 

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



