THE ELASMOBRANCn FISHES 181 



the sharks may it be spoken of as a true anastomoticns. In a type like Scyllium 

 it courses by the spiracular region almost uninterruptedly and passes through 

 a foramen in the orbit to join the internal carotid. In some of the other forms 

 (Acanthias, Zxjgaena, fig. 170) instead of being straight it may pursue a most 

 tortuous course. In these, and in many other forms it is interrupted at the 

 spiracle. In CetorJiinus (fig. 171b), for example, it forms the so-called "won- 



B 



Fig. 171. Arteries associated with the spiracle. 

 A. Raja. (From Hyrtl.) B. Cetorhinus. (From Carazzi.) 

 i.e., internal carotid artery; op., optic artery; p.s., pseudobranchial artery; r.a., ramus 

 anastomoticns. 



der net," the wonder net being composed of a coil of arteries connecting the 

 part going to the spiracle with the part leaving it. 



A different condition is found in this artery in the rays. In these the spiracle 

 is usually large and the blood supply to the filaments is better developed than 

 in the sharks. The artery here takes its origin similarly from the first efferent- 

 collector and as a large vessel (ps., fig. 171a) passes toward the pseudobranch. 

 Before reaching the latter, however, it gives off a large branch to the adductor 

 mandibularis muscle. At the pseudobranch it separates into numerous fila- 

 mentous arteries, and then continues as a smaller artery (r.a.) to join the 

 internal carotid artery (i.e.), as in the sharks. On its way it gives off the 

 ophthalmica magna to the eye. 



]Much attention has been given to the function of the ramus anastomoticns. 

 In some of the sharks in which the spiracle is closed and in w^hich the artery 

 passes almost directly from the collector to the internal carotid, it is a true 

 ramus anastomoticns. But in the rays it is composed of an afferent and an 

 efferent part. It has been urged by Hyrtl (1858) that in the rays the branch 

 connecting the internal carotid and the spiracular gill is the afferent branch 



