5 8 HYPOPHYSIS->OVARY-> OVIPOSITOR II 



6. Platy- and leptobasia. 



The hypophysis constitutes an aggregate of glandular parts 

 developing from the roof of the mouth the lobus tuberalis, 

 anterior and intermedius, to be called the adeno-hypophysis, 

 and one part developing from the brain, namely, the lobus 

 posterior or neuro-hypophysis. We can usually recognize a 

 protuberance of the third ventricle through the infundibu- 

 lum, as recessus infundibuli, in the lobus posterior. This 

 connexion between the hypothalamus and the hypophysis, 

 known as the pituitary stalk, may be present in fishes in the 

 form of a thin stem. In this case we say that the hypophysis 

 " is leptobasic (Fig. 50B), as in Rhodeus amarus, Carpiodes 

 cavpio, Carassius autatus, Lophius piscatorius, with its long 

 thin stalk is the extreme case. When this connexion, how- 

 \cver, is so short that we cannot speak of a genuine stalk, and 

 j the hypophysis seems to be attached to the bottom of the 

 ^hypothalamus, then the hypophysis is platybasic, as in 

 Pettomyzon, Micropterus, and others (Fig. 51B). Between 

 these two extremes various transitional forms may be 

 observed with short, broad hypophysis-stems, as in Leuciscus, 

 Zoarces, Anguilla, Fundulus, and others. 



c. Position of the hypophysis stem and the hypophysis 

 axis. 



The hypophysis does not always hang at right angles under 

 the hypothalamus, but owing to a shift of its longitudinal 

 axis may assume different positions with respect to the axis 

 of the animal body. 



The point at which the stalk enters the body of the hypo- 

 physis may be dorsal; the dorsobasal type (Fig. 50B), and 

 as such may be found either in front (Rhodeus), in the centre 

 (Leuciscus, Anguilla, Fundulus) , or towards the back 

 (Esox, Lebistes, Carassius). Owing to a shift of the longi- 

 tudinal axis of the hypophysis, through which the hypo- 

 physis is directed backwards, the point of entry of the hypo- 

 physial stalk may be displaced considerably more towards the 

 front, producing the craniobasal type, as in Zoarces, Carpio- 

 des, and Lophius. The cranial or caudal shift of the axis is 



