FISHES. 325 



It does not at all fill the cavity, and the interval between the pia 

 mater which nearly binds it, and the dura mater, which lines the 

 interior of the cranium, is occupied only with a loose cellular tissue, 

 or a sort of arrachnoid, that is frequently impregnated with an 

 oil, or even sometimes, as in the sturgeon and the tunny, with a very 

 compact fat. 



It has been observed that this space between the cranium and the 

 brain is much less in the young fishes than in the adult ones, a proof 

 that their brain does not grow in the same proportion as the rest of 

 their body, and we have actually found its dimensions very nearly the 

 same in species in which one was, in other respects, double the other. 



The lobes composing the brain are placed in succession, and repre- 

 sent very often a sort of double chaplet. There are also tubercles, 

 and these sometimes are pretty numerous, which are hidden in the 

 interior or beneath one of the great lobes*. 



To come to the knowledge of the analogy between these various 

 lobes and tubercles with those of the brains of the other classes, we 

 must first start from a fixed point, and this we shall make the cere- 

 bellum, (a, pi. VI, fig. V. VI, VII, and IX). 



This is a portion respecting the nature of which no misunderstand- 

 ing can arise, for it is characterized by having no fellow, and having 

 its position across the upper part of the spinal marrow, and is joined by 

 the sides so as to resemble a bridge. 



In front of this cerebellum may be seen without dissection, on the 

 superior surface, a first pair of lobes (b, b, ib,) the interior of which is 

 permanently hollow, and which are preceded by one and sometimes by 

 two other pairs (c, c, ib,) which are generally solid. In the interior 

 of the hollow lobes upon their floor, and in front of the cerebellum, 

 are often one or two pairs of small tubercles (d, ib, fig. IX). At the 

 inferior surface, there are, under the hollow lobes, another pair of 

 protuberances (e, e, ib, fig. VIII), which we call inferior lobes ; and 

 between them, in front, is suspended an azygos body ff,) which cor- 

 responds to what is called the pituitary gland. Behind the cerebellum 

 are other lobes (g, g,) different in number and formation, of which the 

 superior class offers nothing except its vestiges, and which we call the 

 posterior lobes. 



Certain anatomists take the hollow lobes for the hemispheres of the 

 brain, the lobes placed too far in front for the analogues of the olfactory 

 protuberances of the superior class, and the inferior lobes to be ana- 

 logous to the optic lobes of birds; others consider the inferior lobes 

 as analogous to the mamillary protuberances of the mammalia, the 

 hollow lobes as those of the optic lobes of birds ; they place the brain, 

 properlv so called, in the anterior lobes, notwithstanding their minute- 

 ness and simplicity, and seem inclined to admit only the olfactory 

 protuberances in the lobes which sometimes precede them there, or 



* The brain of the perch is represented in its natural situation, with the nerves 

 of the head and shoulder, pi. VI, fig. V ; it is figured separately by its superior 

 surface, ib, fig. VI ; laterally fig. VII; from below fig. VIII. At figure IX, the 

 plate represents the hemispheres opened, and the cerebellum put aside after having 

 cut one of its connections. The superficial nerves of the body are represented with 

 the muscles PI. IV (the first of Myology) and the deep seated nerve* PI. V. 



