992 



PISCES. 



tion at the opposite side of the vascular circle. 

 The branches which afterwards unite to form 

 the single pulmonary artery on each side are 

 given off from near the termination of the 

 second and third pairs of the primitive aortic 

 trunk, which thus combine the functions of 

 both systemic and pulmonary arteries. The 

 pulmonary artery, formed by the union of the 

 branches from the second and third branchial 

 arteries, descends between the vena cava (Jig. 

 525, e) in front, and the left branch of the 

 vena pulmonalis (f) behind to the interspace 

 to the lungs; here it distributes branches to the 

 anterior lobes, and then divides; each division 

 extends along the mesial side of its correspond- 

 ing lung to the extremity. The blood distri- 

 buted by the capillaries of this artery over the 

 cells of the lung is collected into a vein (ri) 

 which returns along the lateral or outer margin 

 of the lung as far as the commencement of the 

 lobulated part; here it crosses obliquely the 

 anterior surface of the lung and unites with its 

 fellow. The common pulmonary vein runs 

 parallel with and behind the vena cava for a 

 few lines, then obliquely pierces the pericar- 

 dium, and enters the sinus formed by the ex- 

 pansion of the vena cava, and continues attached 

 to the parietes of that sinus till it reaches the 

 auriculo-ventricular aperture, where it termi- 

 nates close behind the cartilaginous knob 

 before mentioned.* 



Portal system of veins. All the blood de- 

 rived from the stomach, from the intestines, 

 and from the spleen, is collected into one or 

 sometimes into several trunks, which convey it 

 into the liver for the elaboration of bile pre- 

 cisely as in other races of Vertebrata. In some 

 genera, however, more especially the C'/pri- 

 nid<e, the lobes of the liver are so intervolved 

 with the intestinal folds, that the venous blood 

 from the intestines enters the liver through 

 innumerable small branches, none of which 

 are of sufficient size to be regarded as a main 

 trunk of the portal vein. Rathke,f indeed, 

 observes, in relation to this subject, that 

 the vena portae of Fishes exhibits a kind of tran- 

 sition in its arrangement, a sort of tendency to 

 perfection indicated by progressive concentra- 

 tion of the venous trunks according to the fol- 

 lowing scale: As an improvement upon the 

 portal system of the Ciprinidee, in Cottus scor- 

 pio all the veins bringing the blood from the 

 abdominal viscera form three principal trunks, 

 which enter the liver separately. In Cobitis 

 fossilis most of these veins are found united 

 into two trunks, which penetrate the liver sepa- 

 rately ; but besides these there are some strag- 

 gling branches which keep themselves inde- 

 pendent of the two great veins. In the Blemiy 

 and the Pike there are only two portal trunks. 

 In the Lump-fish, the Shad, &c., the two 

 trunks are united into one; but there are still 

 small veins which run isolatedly into the sub- 

 stance of the liver; and lastly, in the Eel, the 

 Perch, &c., there is only one vena portae, as in 

 the most highly organized vertebrate animals. 



* See Professor Owen's paper, ubi supra, 

 t Annales des Sciences Nat. torn. ix. p. 170. 



There is a remarkable circumstance connected 

 with the great venous trunk above alluded to 

 which accompanies the spinal cord lodged in 

 the superior vertebral canal, for this vein, al- 

 though it receives a good proportion of the 

 blood derived from the muscles of the upper 

 part of the trunk, does not empty itself into the 

 venous sinus of the heart, and, from the circum- 

 stance of its giving off numerous large branches 

 to the substance of the kidney, has been re- 

 garded as forming a renal portal system, similar 

 to that described by Jacobson as existing in 

 Birds. It must, however, be observed that this 

 superior vein communicates ^ery freely with the 

 inferior vein, which indubitably represents the 

 vena cava inferior, and consequently the renal 

 branches may be derived from, and not distri- 

 buted to, the kidney. 



Lateral system of vessels. Dr. Marshall 

 Hall discovered some years ago a pulsating 

 cavity or heart situated near the caudal extr,e- 

 mity of the vertebral column of the Eel, the con- 

 tractions of which were found to be quite inde- 

 pendent of the pulsations of the branchial heart, 

 tin's organ beating 160 times in a minute, while 

 the pulses of the branchial heart were only 60. 

 This structure, the existence of which only was 

 pointed out by Dr. Marshall Hall, has since 

 been carefully investigated by M. Hyrtl,* 

 and the following is the result of that gentle- 

 man's explorations. The organ in question is 

 easily seen by stretching out the tail of an Eel 

 upon a piece of glass, to which it readily ad- 

 heres owing to the viscid secretion furnished by 

 the skin. Its pulsations are very lively, and it 

 seems surrounded by a transparent areola, which 

 appeared to M. Hyrtl to consist of two sacs. 

 The disorganization of the spinal marrow by 

 means of a wire had no effect upon the number 

 of its pulsations, and even when the branchial 

 heart was tied or the animal cut in two, the 

 caudal heart continued to beat for five or six 

 minutes. The genera in which the caudal 

 heart and the apparatus connected with it 

 were examined, were Accipenser, Salmo, Perca, 

 Abramis Leuciscus, Gadus, Gobio, Sifurus, 

 ESOJC, Cyprinus, Zeus, Lophius, and several 

 others, so that doubtless the system under 

 consideration is common to the whole class of 

 Fishes. 



Brain. The enceplialon of Fishes is remark- 

 able for its diminutive size in proportion to the 

 dimensions of the animal, and also with rela- 

 tion to the nerves which are derived from it ; 

 in fact it occupies but a very small portion of 

 the cavity of the cranium, the wide interval exist- 

 ing between its surface and the dura mater that 

 lines the cranial parietes being filled up with 

 loose cellulosity rilled with fluid, and some- 

 times containing abundance of oil, or in certain 

 instances, as for example in the Sturgeon and 

 Tunny, of a compact and fatty substance. 



It has been remarked that this interval be- 

 tween the cranium and the surface of the brain 

 is much less in young subjects than in adults- a 



* Archiv. fur Anat. Phys. und Wissenschaftliche 

 Medecin herausgegeben von J. Muller. 1843. p. 

 124. 



