478 The Animal Kingdom 



Externally the elongated body is composed of an anterior head 

 and a slender trunk. The general orientation of the body parts is like 

 that of the other molluscs. The body is elongated dorsoventrally and 

 compressed anteroposteriorly. Thus the tentacles are ventral and cor- 

 respond in position to the foot of the pelecypods. The head has a cen- 

 tral mouth surrounded by ten sucker-bearing arms. One pair of these 

 arms is longer than the others and is retractile. These function as 

 tentacles. The head also has two large well-developed eyes complete 

 with retina, lens, and cornea. 



SUCKCR- 



CARTILAGC . 

 ESOPHAGUS. 



MUSCLE- 



ANTERIOR AORtA 



CUT SURFACE OF MANTLE. 



SYSTEMIC HEART 



MANTLE ARTERY. 



VISCERAL MASS 



.RECTUM 



.MANTLE 

 PENIS 



^CILL 



BRANCHIAL VEIN 



.BRANCHIAL ARTERY 

 _ BRANCHIAL KBAHT 



Fig. 157. — Anatomy of the squid, Loligo; a portion of the body wall is removed. 



Surrounding the internal organs is the mantle. At its free end 

 it forms the collar. Below this neck region is a funnel, the siphon. 

 At the dorsal end of the mantle are triangular fins. 



