HEART 



363 



(Kathke) and Gymnarchus (Assheton). The intestine becomes 

 lengthened and sometimes much coiled. The pancreas almost dis- 

 appears. The pyloric caeca vary greatly in development (Fig. 350). 



Already in Amia the bulbus arteriosus (base of the truncus) of 

 the heart is large and the conns small, in the Teleostei the non- 

 contractile bulbus is still larger and the conns reduced to a mere 

 vestige bearing a single row of valves. A larger remnant of the conns 

 with two rows of valves occurs in Albula (Butirimis) and Osteoglossum 

 (Boas [39]), and in Tarpon and Megalops (Senior [405]) (Figs. 69, 303). 



Many variable and minor differences occur in the vascular 

 system [8, 314, 131, 417, 360]. The lateral epigastric veins dis- 

 appear, or may be represented by a prolongation of the hepatic 



Fio. 



.Median longitudinal section of tin' brain of a Trout (>Wm..). AH, aqueduct.!!* Sylvii ; Bo, 

 olfactory lobe ; Cbl, cerebellum; C.c, central canal of spinal cord; Cm, anterior commissure; 

 Cho, optic nerve ; Ci, inferior commissure ; <;t/i, pineal body ; Ily and Hy', hypophysis ; J, 

 infundibulum ; Nol, olfactory nerve ; Pa, roof of telencephalon ; pf, velum transversum ; S.v, 

 saccus vasculosus ; 2Vo, pia mater ; Ti, roof of mid-brain ; tr, crossing fibres of fourth nerve ; 

 V.c, valvula cerebelli ; !'/. ventricle of telencephalon; I';/, fourth ventricle; Vt, third 

 ventricle. (After Rabl-Riickhani. from Sedgwick's Xnnlng-ii.) 



portal into the caudal vein. Direct communicating vessels through 

 the kidneys to the posterior cardinals tend to reduce the renal 

 portal system (Fig. 351). The vascular supply of the air-bladder 

 has been described above (p. 226). 



The chief modifications in the brain have already been men- 

 tioned (p. 305). It is to be noticed that it is much concentrated, 

 and in spite of the great development of the hinder parts, the 

 prosencephalon is scarcely differentiated and has an epithelial roof. 

 The valvula cerebelli attains its greatest development, and the optic 

 lobes may be huge. The Teleostei are distinguished by the absence 

 of an optic chiasma, the optic nerves crossing each other outside the 

 brain without mixing (Figs. 352-53). 



