170 THE SPINY DOGFISH -THE SKATE 



(peritoneal or abdominal cavity) by the pericardio-peritoneal canal, which 

 opens in front, in the middle line, above the sinus venosus. Find this opening, 

 and pass a seeker along the canal (on the ventral surface of the oesophagus). 



Make a complete sketch showing the heart, ventral aorta, arid afferent 

 branchial vessels. 



[In the Skate the heart also consists of four parts — viz. the sinus venosus, 

 auricle, ventricle, and conus arteriosus or pylangium. Connected with the anterior 

 end of the pylangium is the synangium or buWus arteriosus, which gives off the 

 median ventral aorta. The ventral aorta passes forwards in the middle line 

 and gives 'off the anterior and posterior innominate arteries. Each anterior 

 innominate artery divides into two afferent branchial vessels which convey blood 



Pylangium' 

 Auricle - 



Sinus venosus 



Synangium 

 Ventricle 



•Pericardial 

 cavity 



Fi«. 57. — The Afferent Branchial or Ventral Arterial System 



of the Skate {Baia). 



I. Anterior Innominate Artery ; H. Posterior Innominate Artery. 



to the half-gill of the hyoid arch and the gill of the first branchial arch. The 

 posterior innominate artery divides into three branches conveying blood to the gills 

 of the second, third and fourth branchial arches.'] 



2. The Efferent Branchial Vessels and Dorsal Aorta. 



Cut through the angle of the mouth on the right side and carry the incision 

 backwards through the middle of the gill-clefts of that side. Turn the whole 

 of the lower jaw over to the left side, and wash out the mouth. Carefully 

 remove the mucous membrane from the roof of the mouth, working from the 

 oesophagus forwards. The efferent branchial vessels will then be seen. There 

 are four pairs, and thesis all join to form the median dorsal aorta, which passes 

 backwards along the mid-dorsal line of the body. Trace each efferent vessel 

 from the aorta to the gill. In Acanthias the first pair of efferents unite just 

 between the fourth gill-clefts. From each a small artery is given off which 

 soon disappears into the cartilage. This vessel probably corresponds to the 

 vertebral artery of the Skate. Where the first efferent vessel forms a loop 

 around the first branchial cleft, it gives off an artery corresponding to the 

 common carotid of Raia and Scyllium. This common carotid runs along 



