280 ANATOMY OF VERTEBRATES. 



their inferior interspace a vascular medullary depressed sac (the 

 ' hsematosac,' fig. 185, o), usually oblong, as in the Cod, rarely 

 bifid or cordiform, as in the Lumpfish. These prominences from 

 the floor of the mesencephalon, posterior to the infundibulum and 

 hypophysis, ih.p, are peculiar to the brain of fishes, and, in their full 

 developement, are restricted to the typical osseous member of the 

 class ; they are absent in the lowest, and disappear in the highest 

 orders ; they are mere rudiments, or are wanting, in the Poly- 

 pterus, as in the still more amphibioid Lepidosiren. 



The true vasculo-membranous infundibular downward pro- 

 longation of the third ventricle exists in all Osseous Fishes, and 

 extends from the anterior angle of the hypoaria, where these 

 exist : the infundibulum is commonly short and thick, so that the 

 hypophysis is almost sessile, as in the Cod ; but in the Lophius, 

 the infundibulum is longer than the entire brain, and the hypo- 

 physis lies at the fore-part of the cranial cavity, far in advance of 

 the cerebral lobes. 1 In the Cod the hypophysis, fig. 185, 7?, is a 

 subspherical mass, with an irregular or slightly nodulated surface, 

 almost half the size of the human, so called, ' pituitary gland,' 

 and illustrating the vast proportional size of this constant 

 appendage to the brain of Fishes. In the Lepidosiren the infun- 

 dibulum is wide, and the hypophysis a white flattened discoid 

 body, fig. 186, o. 2 In all Fishes it is richly supplied with vessels, 

 and is closely attached to the floor of the cranium ; but, although 

 its early developement checks or modifies that of the cranial 

 vertebras, it is not provided with a special chamber or ' sella.' 

 The prolongations of the fibres from the mesencephalon which 

 expand into the prosencephalic or proper cerebral lobes rarely 

 show any preliminary developement of ' thalami ; ' but the parts 

 homologous with those recruiting ganglia are constantly indicated 

 by the attachment of the conarium, or upper prolongation of the 

 third ventricle. 



The conarium, figs. 175, 186, 187, tc, is as constant an append- 

 age of the encephalon in Fishes as the hypophysis ; but it is com- 

 monly only a vasculo-membranous pyramidal sac continued from 

 the third ventricle, the base expanding from between the anterior 

 interspace of the optic lobes, and the apex directed forward and 

 attached to the roof of the cranium. Some medullary matter 

 mingles with the membranous walls of the conarium in the 

 Clupeoid and Cyprinoid Fishes : in some Fishes there is grey 

 matter in the conarium : in most it is membranous only, as in the 



1 lx. p. 56. t. ii. fig. 1. 



■ The hypophysis is marked g in xxxiii. pi. 27, fig. 4; and is called ' mammillary 

 hody' in Lepidosiren tuuiectens, ib. p. 361. 



