DEVELOPMENT OP THE HEAD IN GOBTUS CAPITO. 337 



double the latter. The figure shows that the brain of Gobius 

 at this age bears considerable resemblance to the brain of a 

 human embryo of the third week as depicted by His (7), ex- 

 cept that the fish does not possess the sharp curve in the 

 region of the mid-brain. The chorda extends as yet only to 

 below the cerebellum^ and the central cavity of the brain is 

 but partially formed. This cavity appears first in the region 

 of the optic stalks, and generally in the ventral half of the 

 neural cord. 



Pore-brain, mid- brain, and hind brain are already indicated 

 by slight constrictions. In the hind brain can be distinguished 

 cerebellum and medulla oblongata. The mid-brain already 

 shows the preponderance characteristic of Teleostei. It is 

 slightly moulded to the shape of the eyes, which appear to be 

 relatively larger in Gobius than in Salmo. The fore-brain 

 diff'ers somewhat from that of other Teleostei, and shows some 

 peculiarities which deserve special attention. Ventrally a 

 bulging of the floor indicates the commencement of the in- 

 fundibulum. Behind this point, as will be shown later, the 

 premandibular mesoderm is continuous across the middle line. 



In front of the infundibulum is a constriction where the 

 optic chiasma comes to lie subsequently. The foremost ventral 

 portion of the brain is a rounded prominence which gives rise 

 laterally to the optic stalks and eyes. At the extreme anterior 

 end the wall passes inwards to form with the corresponding 

 upper portion of the brain a well-marked indentation. 

 The nasal organs lie above and in front of the optic stalks, 

 both nose and eye being as yet directed outwards and slightly 

 upwards. That portion of the brain lying between the nasal 

 organs is the region of the corpora striata. Figs. 5 and 6 

 represent sagittal and transverse sections of the anterior end 

 of the brain. In fig, 6, whose position is indicated in the 

 diagram [a, a, fig. 2), both upper and lower portions of 

 the brain are cut in section where they separate to form 

 the above-mentioned indentation. The upper portion, the 

 corpus striatum, is oval in section, the long axis being dorso- 

 ventral. The lower is more rounded. In the corpus striatum 



