150 MUSCULAR SYSTEM. 



and strong, on the long feet of the octopods, as the argonauts 

 and the octopus, they adhere to external objects by the close 

 application of their thick muscular margins, and by forming 

 a partial vacuum in their centre. By these organs the cepha- 

 lopods can creep upwards on a vertical surface, even when 

 out of the water. The octopus, destitute of any lateral fins, 

 is assisted in swimming by muscular membranes extended 

 between the bases of the feet ; this animal swims backwards 

 by impelling the water forwards, but the species which have 

 lateral fins extending from their trunk can swim with ease 

 either forwards or backwards, and they appear to spring up- 

 wards sometimes, to a distance from the surface of the sea. 

 These predacious animals have very powerful muscles con- 

 nected with the mastication of their food, as well as with its 

 prehension. Large sphincter muscles, with a fimbriated 

 fleshy lip, surround the entrance of the mouth, and strong 

 retractor muscles of the jaws are inserted around the reso- 

 phageal opening of the cranium. The bases of the jaws are 

 surrounded with superimposed strata of powerful compressor 

 muscles, and the short, thick, fleshy tongue, covered with 

 numerous rows of sharp, conical, horny spines, is moved by 

 strong muscles attached to a rudimentary os hyoides. The 

 maxillary apparatus is also provided with two lateral rotator 

 muscles, which pass forwards to be inserted into its anterior 

 part. 



FIFTH SECTION. 



Muscular System of the Spini-Cerebrated or Vertebrated 



Classes. 



The muscular system is placed on the exterior of the hard 

 parts in the vertebrated animals ; its fibrous structure is 

 here the most distinct and irritable, and its separate muscles 

 and fasciculi are most obvious and defined. The muscles 

 have generally a red colour, from the red blood sent through 

 them, and they are connected with the bones, for the most 

 part, by tendinous prolongations. They are most pale, soft, 



