760 STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 



brain, is the most satisfactory, the other figures being in many 

 respects inaccurate; but even Wilder's figure and description, 

 though taken from the fresh object, appear to us in some 

 respects inadequate. He offers, moreover, fresh interpretations 

 of certain parts of the brain which we shall discuss in the sequel. 



We have examined two brains which, though extremely soft, 

 were, nevertheless, sufficiently well preserved to enable us to 

 study the external form. We have, moreover, made a complete 

 series of transverse sections through one of the brains, and our 

 sections, though utterly valueless from a histological point of view, 

 have thrown some light on the topographical anatomy of the 

 brain. 



Plate 38, figs. 47 A, P, and C, represent three views of the 

 brain, viz.: from the side, from above, and from below. We will 

 follow in our description the usual division of the brain into fore- 

 brain, mid-brain, and hind-brain. 



The fore-brain consists of an anterior portion forming the 

 cerebrum, and a posterior portion constituting the thalamen- 

 cephalon. 



The cerebrum at first sight appears to be composed of (a) 

 a pair of posterior and somewhat dorsal lobes, forming what have 

 usually been regarded as the true cerebral hemispheres, but 

 called by Wilder the prothalami, and (b} a pair of anterior and 

 ventral lobes, usually regarded as the olfactory lobes, from which 

 the olfactory nerves spring. Mainly from a comparison with 

 our embryonic brains described in the sequel, we are inclined to 

 think that the usual interpretations are not wholly correct, but 

 that the true olfactory lobes are to be sought for in small enlarge- 

 ments (Plate 38. figs. 47 A, B, and C, off.) at the front end of the 

 brain 1 from which the olfactory nerves spring. The cerebrum 

 proper would then consist of a pair of anterior and ventral lobes 

 (ce.}, and of a pair of posterior lobes (ce'.\ both pairs uniting to 

 form a basal portion behind. 



The two pairs of lobes probably correspond with the two 

 parts of the cerebrum of the Frog, the anterior of which, like 

 that of Lepidosteus, was held to be the olfactory lobe, till Gotte's 

 researches shewed that this view was not tenable. 



1 The homoiogies of the olfactory lobes throughout the group of Fishes require 

 further investigation. 



