14 



around the eyes and are distributed to the regions of the mandible 

 and snout. Do not, at present, trace them beyond the posterior 

 edge of the eye. 



Another vessel arises from the middle of the anterior side- of 

 the first efferent branchial loop and runs forward to the spiracle, 

 where it ends in the capillaries of the pseudobranch. This is the 

 afferent hyoidean artery. The term pseudobranch is used for the 

 branchial lamellae of the spiracle rather than demibranch because 

 of the arterial blood supply of this organ. 



Immediately after uniting the internal carotids divide and di- 

 verge, forming an X-shaped figure. Each anterior limb of the X 

 again divides into two branches. The lateral branch passes to the 

 ventral surface of the skull; it presently gives off an anterior twig 

 (ophthalmic artery] which enters the eye. It then passes on as the 

 efferent hyoidean artery to the pseudobranch. The inner of the two 

 branchs mentioned above passes on as the internal carotid, sensu 

 strictu, and is distributed to the brain. 



If the dissection is made with care, the branches of the internal 

 carotid can all be found without cutting any important nerves. The 

 branches passing to the eye and brain are best traced to their ter- 

 minations in connection with the dissection of the nervous system. 



Near the union of the first pair of efferent branchial arteries a 

 small posterior vertebral artery arises from each, and runs anter- 

 iorly along the vertebral column. 



Near the divisions of the common carotids two anterior vertebral 

 arteries arise from these vessels and pass posteriorly, often anasto- 

 mosing with the posterior vertebral arteries. These vertebral arteries 

 are vestiges of the former anterior part of the dorsal aorta (compare 

 with Eugaleus, in which the dorsal aorta sends forward two vessels 

 which join the common carotids). 



An oesophageal artery springs from the second efferent branch- 

 ial, and passes back until it enters the wall of the oesophagus. It 

 also gives off nutrient branches to the second, third, and fourth 

 gill pouches. The nutrient artery of the first gill pouch arises di- 

 rectly from the first efferent branchial. 



Near the point at which the fourth pair of efferent branchials 

 join the aorta, two small subclavian arteries leave the aorta and 

 pass into the pectoral fins. There is some variation in regard to 

 the point of origin of these vessels; it may be either in front of or 

 behind the junction of the fourth efferent branchials. with the aorta. 



The hypobranchial artery passes along the ventral ends of the 

 gill pouches. It is either connected with the efferent branchial loops 

 by short branches, or is formed, in part at least, by short vessels 

 connecting these loops. The hypobranchials are important nutrient 

 vessels, supplying the gill pouches and the muscles of the throat 

 and the oesophagus by means of numerous small arteries; from the 

 hypobranchials also arise small posterior coronary arteries which 

 pass to the ventral and posterior walls of the pericardium and the 

 sinus venosus, and larger anterior coronary arteries supplying the 

 ventricle and conus arteriosus. The hypobranchials can frequently 

 be followed along the dorsal side of the pericardium and then out- 

 ward to junctions with the subclavian arteries. 



The coeliac artery (coeliac axis) arises from the aorta just back 

 of the subclavians. Passing posteriorly and ventrad close to the 

 right side of the stomach and reaching the gastro-hepatic omentum, 

 it divides into two branches, the gastro-hepatic and anterior intes- 

 tinal arteries. The first gives off a small hepatic artery to the liver 



