FISHES. 31 



a fine network of capillaries on the gills. From this the roots of the 

 branchial veins arise, which mounting along the branchial arches, 

 afterwards unite to form the large artery. Hence in fishes a system 

 of capillaries is placed between the heart and the aorta; and this is 

 one of the most characteristic peculiarities in the anatomy of this 

 class. 



Already from the branchial veins, before they unite to form the 

 aorta, certain arteries arise especially for the head. In the bony 

 fishes the branchial veins of each side first unite to form a vein 

 {ve7ia hrancMalis communis), and pass backwards into the aorta, 

 whilst, according to the discovery of Hyetl, they are united in front 

 by a transverse vessel, and thus form an arterial circle [cir cuius 

 cephalicus) beneath the cranium \ The arteries [arterice axillares) 

 for the anterior limbs (pectoral fins) are, in Torpedo and Chimcera, 

 provided with a muscular covering and expanded into lateral hearts^. 

 In Anvphioxus lanceolatus, where the heart is not enclosed in a 

 pericardium and is tubular, contractile swellings have also been 

 observed on the branchial arteries, and, moreover, on each side 

 a pulsating arch, which passes immediately from the heart to the 

 ao7'ta^. 



The venous system also of fishes may be illustrated by the 

 history of development in higher vertebrate animals. This teaches 

 us that originally there are two anterior and two posterior venous 

 stems which conduct the blood back to the heart. The anterior are 

 the persistent vence jugulares ; the posterior, which, at a later period, 

 when the cava is developed, in great part disappear, are named by 

 Rathke vence cardinales. On each side the anterior and posterior 

 venous stems meet in a transverse canal {Ductus Cuvieri), which 



^ Similar in form to the arterial circulus Willisii within the human skull. — The 

 work of Htrtl on the vascular arrangement of fishes {Medic. Jahrh. cler (Estterr, 

 Staates. Neueste Folge, Bd. XV. 1838) is known to me, and perhaps to many others, from 

 citations alone. Compare also on this subject, J. Mdeller in Ahhandl. der Kd7i,igl. 

 Akad. der Wissensch. zu Berlin, aics d. J. 1839, y^W^- Anatomic der Myxinoidcn, dritte 

 Fortsctzung. This entire work is published separately, Berlin, 1835 and 1841. 



^ According to J. Davy in Torpedo, Phil. Trans. 1832, p. 259; according to the 

 investigations of DuvEENOT, and afterwards of Valentin in Chimcera, Ann. des So. 

 natur., sec. S^rie, viii. 1837, pp. 35 — 41, Mueller's Archiv, 1842, s. 25. 



3 Here also the portal vein and the cava are pulsating tubular hearts. See Muel- 

 ler Uebcr den Bail untl die Lebenserscheinungen der Branchiostoma luhricum. A hh. der 

 Konigl. Akad. der Wisscnschaft. zu Berlin aim d. Jahre 1844. 



