AFFERENT BRANCHIAL VESSELS. 255 



(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 afferent branchial vessels are most easily found by 

 making a median incision through the muscles in front of the 

 pericardium, and parting the muscles gently till the thyroid body 

 a red oval body is found : this overlies the anterior end of 

 the cardiac aorta, which may then be dissected backwards with 

 care, so as to avoid injuring the afferent vessels, which it gives 

 off, and which must now be followed up to the gills. 



a. The cardiac aorta is a direct continuation forwards 



of the conus arteriosus. It is little more than an 

 inch in length, and gives off laterally the five 

 pairs of branchial arteries. 



Note the thyroid gland lying just over the anterior end of the 

 cardiac aorta. 



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. 53. Scyllium catulus. 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 left half turned outwards. 

 The lower jaw, the lower portion of the hyoid arch, 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. The thyroid gland is not shown, (c. h. h.) 



AA, pericardial cavity. AE, sinus venosus. AF, auricle. AH, ventricle. 

 AK, conus arteriosus. AL, AM, and AN, first, second, and third branchial 

 arteries, in hyoid and first and second branchial arches respectively. AO, car- 

 diac aorta. CA, hyoidean artery. CE, external carotid artery. CP, internal 

 or posterior carotid artery. CV, carotid artery. EA, post-spiracuiar artery. 

 EB, anterior limb of first efferent branchial loop. EC, communicating vessel 

 between second and third efferent branchial loops. EE, fourth epibranchial 

 artery, bringing blood from gills of fourth and fifth clefts. HA, dorsal aorta. 

 HE, subclavian artery. HF, cceliac artery. NA, nostril. NE, nasal flap: 

 in this species the two flaps are not united as in S. canicula. o, eyeball. TA, 

 hyo-mandibular cartilage cut across. VA, spiracle with pseudo-branch. VE 

 and VF, first and fifth branchial clefts. W, pectoral girdle cut across, with a 

 portion of the muscles of the pectoral fin. 



