802- 



COMPARATIVE ANATOMY 



Fig. 454. 



A, The forepart of the body of a dogfish, dissected to show the heart and 

 ventral arterial system, a.b.a., Afferent branchial arteries ; em., auricle ; c.a., conus 

 arteriosus ; ch, ceratohyal cartilage ; d.C., ductus Cuvieri ; g., gills ; y.c., gill clefts ; 

 i.e., internal opening of the first gill cleft ; M.c., Meckel's cartilage ; mu. muscles 

 from coracoid region of shoulder girdle to various parts of visceral skeleton ; 

 pm., pericardium; s.v., sinus venosus ; sc. f scapula; thy., thyroid gland (dis- 

 placed) ; v., ventricle; v.ao., ventral aorta. 



B, The forepart of a dogfish, dissected from the ventral side, to show the 

 dorsal arterial system, the olfactory organs, and certain structures in the orbits. 

 The middle part of the floor of the -mouth has been removed, a.b.a., Afferent 

 branchial arteries ; c.c., common carotid artery ; coe.a., creliac artery ; d.ao., dorsal 

 arota ; e.b.a., efferent branchial arteries ; e.c., external carotid ; en., nostril ; 

 epibr., epibranchial artery ; hm., hyomandibular cartilage ; hy.a., hyoidean artery ; 

 i.e., internal carotid arteries ; inf., infundibulum ; M.c., Meckel's cartilage in lower 

 jaw ; o.i., inferior oblique muscle ; o.s., superior oblique muscle ; olf.o., olfactory 

 organ; p.c., -posterior carotid artery; sc., scapula; scl., subclavian artery; sic., 

 skull ; sp., spiracle ; V.md., V.mx., mandibular and maxillary branches of fifth 

 nerve; //., optic nerve. (After Borradaile.) 



through the branchial arches. This involves as many pairs of branchial 

 arches as there are paired functional afferent vessels carrying blood to 

 the gills, and efferent vessels carrying the oxygenated blood from the 

 gills to the dorsal aorta. 



AMPHIBIA (Figs. 446, 456) 



The principal changes in the amphibian circulation are concerned 

 with the branchial arches. These are remodeled to become blood ves- 

 sels that can function in an air-breathing animal. The branchial vessels 

 of lobe-finned ganoids and of amphibia in the larval stage consist of 

 four pairs; known from the region in which they develop as the third, 

 fourth, fifth and sixth. The third pair becomes the carotid arteries that 

 supply the head; the fourth becomes the systemic arches that supply 

 most of the body ; the fifth disappears, and the sixth becomes mainly the 



