PISCES 



171 



branchials run up between the gill slits, sending branches into 

 the gill filaments. The blood is by this means brought into 

 close contact with the stream of water which is being constantly 

 during life passed through the gills, and it is arterialised. 

 The arterial blood is conveyed from the filaments into vessels 

 which loop-like encircle the clefts. There are four complete 

 encircling vessels around the first four clefts, and they are 



Ant. innom. a.'^Vent. aorta 



Vertebral a. 



Subclavian a. 



-Coeliaca. 



-Ant. mes. a. 

 -Dorsal aorta 



Sperm, (or 

 - ovar.) a. 

 -Post. mes. a. 



Renal a. 



Iliac a. 

 Caudal a. 



FIG. 88. Raia. Diagrams of arterial, venous, and portal vessels of adult. 



connected by horizontal anastomosing vessels. The fifth arch 

 possesses a half-loop and is similarly connected to the fourth 

 loop. The first loop receives blood from the hyoid. The 

 upper ends of the loops give origin to the efferent branchials, 

 which are directed backwards in the roof of the pharynx to 

 fuse in succession in forming the anterior end of the dorsal 

 aorta. 



From the point of origin of the first efferent branchial 

 there arises the common carotid. The common carotid 

 divides into an external and an internal branch. The two 

 internal carotids join below the brain case, and the vessel thus 

 formed enters the brain case through a minute foramen to 



