CHAPTER XVII 

 VALVULA CEREBELLI 



We purpose in this chapter to refer in a little more detail to the 

 valvula cerebelli, wliich has been mentioned on several occasions in 

 connection with mormyrus and the barbel. The anatomical position 

 of this organ does not render it accessible to experimental biological 

 research ; if efforts were made to ablate tliis organ in the living 

 animal it would be necessary after exposing the tecta optica of the 

 optic lobes to remove them and then to dissect out the valvula from 

 its posterior attachment to the body of the cerebellum. This might 

 be possible in a hardened brain in the dead animal, but it would 

 involve very serious damage to other parts if attempted in the living 

 animal, and the results of such an ablation, as shown by the behaviour 

 of the fish, would be open to justifiably adverse criticism. This 

 being the case it seems that an attempt at understanding the phy- 

 siology of the valvula might be undertaken by a series of anatomical 

 observations on groups of fish closely related, but yet differing in 

 a marked way in their habits and behaviour. 



There has been very little done in this direction, but it may be 

 of some value if the facts already known about this organ be men- 

 tioned, and they may suggest an attack on this problem by other 

 workers. In the cod, Gadus morrhua, the hinder part of the optic 

 ventricle is occupied by a forwardly projecting process of the cere- 

 bellum, the valvula. " This structure is formed by the invagination 

 of the anterior parts of the cerebellum into the cavity of the mid- 

 brain, and thus in sagittal section shows two super-imposed layers — 

 the lower one continuous behind with the cerebellum, and passing 

 in front by reduplication into the dorsal layer. The latter is closely 

 applied to the first and is continuous posteriorly with the liinder 

 margin of the tectum opticum." This description is taken from the 

 physiological catalogue of the Royal College of Surgeons and, 

 accompanying this, are drawings which demonstrate the relations 

 very clearly (page 19). 



If we dissect the brain of a mackerel we find a very different 

 picture. The valvula cerebelli occupies the major part of the 

 cavity of the optic lobes and causes them to appear very large. 



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