530 



ARTERIES OF PISCES. 



FIG. 3C3. DIAGRAMMATIC VIEW OF THE HEAD 



OF AN EMBRYO TELEOSTEAN, WITH THE PRIMI- 

 TIVE VASCULAR TRUNKS. (From Gegenbaur.) 



a. auricle ; v. ventricle ; ubr. branchial 

 artery ; c'. carotid ; ad. dorsal aorta ; s. bran- 

 chial clefts ; sv. sinus venosus ; dc. ductus 

 Cuvieri ; . nasal pit. 



artery to each of the anterior limbs ; from near the anterior end of 



the dorsal aorta a vitelline 

 artery (or before the dorsal 

 aortae have united a pair of 

 arteries fig. 125, Ro/'A and 

 L of A) to the yolk-sack, which 

 subsequently becomes the main 

 visceral artery 1 ; and from the 

 dorsal aorta opposite the hind 

 limbs one (or two) arteries on 

 each side the iliac arteries 

 to the hind limbs ; from these 

 arteries the allantoic arteries 

 are given oft' in the higher 

 types, which remain as the 

 hypogastric arteries after the 

 disappearance of the allantois. 

 The primitive arrangement of the arterial trunks is with a few 

 modifications retained in Fishes. With the development of the gills 

 the vessels to the arches become divided into two parts connected 

 by a capillary system in the gill folds, viz. into the branchial arteries 

 bringing the blood to the gills from the truncus arteriosus, and the 

 branchial veins transporting it to the dorsal aorta. The branchial ves- 

 sels to those arches which do not bear gills, either wholly or partially 

 atrophy; thus in Elasmobranchii the mandibular trunk, which is fully 

 developed in the embryo (fig. 193, lav), atrophies, except for a small 

 remnant bringing blood to the rudimentary gill of the spiracle from 

 the branchial vein of the hyoid arch. In Ganoids the mandibular 

 artery atrophies, but the hyoid is usually preserved. In Teleostei both 

 mandibular 2 and hyoid arteries are absent in the adult, except that 

 there is usually left a rudiment of the hyoid, supplying the pseudo- 

 branch, which is similar to the rudiment of the mandibular artery 

 in Elasmobranchii. In Dipnoi the mandibular artery atrophies, but 

 the hyoid is sometimes preserved (Protopterus), and sometimes lost. 



In Fishes provided with a well developed air-bladder this organ 

 receives arteries, which arise sometimes from the dorsal aorta, some- 

 times from the caeliac arteries, and sometimes from the dorsal section 

 of the last (fourth) branchial trunk. The latter origin is found in 

 Polypterus and Amia, and seems to have been inherited by the 

 Dipnoi where the air-bladder forms a true lung. 



The pulmonary artery of all the air-breathing Vertebrata 

 is derived from the pulmonary artery of the Dipnoi. 



In all the types above Fishes considerable changes are effected in 

 the primitive arrangement of the arteries in the visceral arches. 



1 In Mammalia the superior meseuteric artery arises from the vitelline artery, 

 which may probably be regarded as ;) primitive cffiliaco-rnesenteric arterj'. 



2 The mandibular artery is stated by Gdtte never to be developed in Teleostei, but 

 is distinctly figured in Lereboullet (No. 71). 



