AFFERENT BRANCHIAL VESSELS. 247 



(2) the efferent branchial vessels, which collect the aerated 

 blood from the gills ; and (3) the dorsal aorta, which is formed 

 by the union of the efferent branchial vessels, and conveys 

 arterial blood to the body generally. 



1. The afferent branchial vessels. 



The ajferent branchial vessels are most easily followed by 

 injecting them from the conus arteriosiis, hut this must not be 

 done if the heart is to be dissected in the same specimen. 



Trace the cardiac aorta forwards from the conus arteriosus, 

 andfolloio its branches on the left side to the gills, removing 

 as much of the muscles of the under surface of the head and 

 of the gills as is necessary to expose the vessels thoroughly. 



a. The cardiac aorta is a direct continuation forwards 



of the conus arteriosus. It is a median vessel 

 lying beneath the floor of the mouth and pharynx, 

 and deeply placed in the muscles of the under 

 part of the head. It is little more than an 

 inch in length, and gives off laterally the five 

 pairs of branchial arteries. 



b. The branchial arteries arise in pairs from the 



cardiac aorta, and carry the blood from it to the 

 gills. The two hindmost pairs arise close together 



Fig. 51 Seyllium oatulus. Dissection from below to show the arterial 



system. The floor of the mouth has been cut through a little to 

 the left of the median plane, and the lefthalf turned outwards. The 

 lower jaw, the lower portion of the hyoid arob, and the whole of the 

 branchial skeleton have been removed on the left side. The floor of 

 the brain-case and that of the left orbit have been removed. On 

 the right side the skin and muscles and portions of some of the gills 

 have been removed, (c. h. h.) 



AA, pericavtliiil cavity. AE, sinus venusus. AP, luiricle. AH, 

 ventricle. AK, cuuus arteriosus. AL, A3Vt, and AW, first, second, and 

 third branchial arberies, in liyoid, and first and second branchial arches re- 

 spectively. AO, cardiac aorta. CA, hyoidean artery. CE, external 

 carotid artery. CP, internal or posterior carotid artery. CV, carotid artery. 

 EA, post-spiracular artery. EB, anterior limb of first efferent branchial 

 loop. EC, communicating vessel between second and third efCei-ent branchial 

 loops. EB, fourth epibranchial artery, bringing blood from gills of fourth and 

 fifth clefts. HA, dorsal aorta. HE, subclavian artery. H!F, ccBliac artery. 

 UA, nostril. WEJ, nasal flap : in this species the two flaps are not united as 

 in 8. caniculu. O, eyeball, TA, hyo-mandibular cartilage cut across. VA, 

 spiracle with pseudo-branch. "V".fi'and VP, first and fifth branchial clefts. 

 VV, pectoral giri^e cut across, with a portion of the muscles of the pectoral fin. 



