GREGORY: FISH SKULLS 



313 



system is remarkably different from those of all other fishes; for not only do they have a 

 greater quantity of blood, a much greater number of blood-vessels and a larger heart, but 

 they also have a new and remarkably complex cutaneous vascular plexus, developed as 

 sheets in the lateral muscle, which is the cause of the dark red or nearly black surface color 

 of the muscles under the "corselet." They also have another highly developed local 



B 



Thunnus 



Fig. 192. Thunnus. Top (A) and occiput (B). 



