8 



in a free edge , the collar , which surrounds the neck and thru which a conical 

 muscular tube , the siphon , projects. The collar articulates by three pairs of 

 interlocking surfaces with the visceral mass and the siphon , mesially with the 

 upper surface of the visceral mass (with the nuchal cartilage) and laterally with 

 each side of the siphon. A pair of triangular fins is attached to the dorsal point 

 of the mantle and to three-fifths of the anterior (upper) surface in such a manner 

 that they form a rhomboidal plate. 



The lance-shaped head consists of the true or primitive head and the 

 anterior part of the primitive foot. The back part of the head . representing the 

 true head , is short and is kidney-shaped in cross-section since the posterior 

 surface is hollowed out for the accommodation of the siphon. A pair of large 

 eyes forms almost the entire sides of the true head and an olfactory fold, just 

 behind the eye, projects backward under the collar. The remainder of the head 

 is formed by a circle of ten foot-lobes , comprising eight sessile arms and two 

 tentacles, which are attached to the ventral surface of the true head and which 

 surround the mouth. While the Squid is swimming the arms and tentacles, are 

 pressed together so that they form an acute , thick , horizontal plate which is 

 used alternately as a rudder and as a cutwater. 



The siphon , a conical muscular tube attached to the lower surface of the 

 visceral mass and to the head , projects downward and forward from the mantle 

 chamber between the head and the mantle. A jet of water ejected thru the 

 siphon whose tip may be directed forward or backward propels the squid 

 backward or forward. 



