CALIGOIDEA. 1327 



nished in volume, and exterior to this continuation, two muscles being 

 attached, each by a tendon, to the diminishing portion of the main 

 muscle. Though apparently distinct, these three muscles continue 

 connected, and pass on beyond the sternum of the second pair of nata- 

 tories, where there is a second subdivision of the muscle. We observe 

 an oblique constriction of the wnole (fig. 1/'), below which, the three 

 muscles are continued of nearly their former size, and a fourth is 

 added, exterior to the three. Thus divided, the muscle continues 

 into the abdomen, where the four parts are separately inserted : the 

 exterior pair diverge, and are attached near the base of the abdomen ; 

 the interior are inserted below the centre of the abdomen, directly 

 under the insertions of the extensor muscles of the back ; the two 

 remaining pairs are continued into the terminal abdominal segment, 

 the outer passing beyond the centre of this joint. Another pair of 

 small muscles are inserted in the base of this joint, which arise near 

 the attachment of the interior pair of abdominal muscles. 



The other set of muscles, consisting of two pair, arise a short dis- 

 tance below the sternum of the posterior natatory, exterior to the 

 muscles just described. One pair, the outer, is inserted in the base of 

 the posterior thoracic segment, and the inner, laterally below the 

 centre of the abdomen. 



The lateral motion of these segments is produced by the simulta- 

 neous action of the flexor and extensor of the same side. The insertion 

 of the more powerful of the abdominal muscles below the centre of this 

 segment, in preference to an attachment near its base, enables the 

 animal to give this segment great flexion. When the animal has been 

 attached to the glass out of the water, we have often separated the 

 anterior portion of the body from the glass, till it formed an angle of 

 75° or 80° with the abdominal portion, and generally the animal has 

 succeeded through the action of these muscles in restoring its head 

 again to the glass. 



The muscle (0) on the back (fig. 1 h) may possibly be attached to 

 the muscle (N), and not to the thoracic segment. We have not suc- 

 ceeded, in our dissections, in exposing these muscles, in order to deter- 

 mine this point. 



(1.) Muscles of the Organs of the Anterior Gephdlothoracic Segment. 

 — In the following account, we shall in general describe only the 



