146 MUSCULAR SYSTEM. 



with their muscular organs of motion extended laterally from 

 the sides of the trunk, and placed more anteriorly than those 

 of the naked cephalopods. In the clio australis, (Fig. 67, A) 

 the form approaches very closely to the cephalopodic in the 

 numerous conical, tubular,cephalic tentacula (A,a,a*,) the form 

 of the head (#,) the position of the eyes, and the lengthened 

 cylindrical form of the trunk, enveloped in a closed muscular 

 mantle (d.) The muscular fins (c,) support, on their pectinated 

 surface, the numerous ramifications of the branchial vessels ; 

 so that the motions of these organs promote the aeration of the 

 blood. In the pneumodermon, (Fig. 67. B,) the muscular pro- 

 boscis (0,) and the lateral tufts of tentacula (b 9 ) terminated 

 each by a sucker, are retractile, the muscular arms (c,) are ex- 

 tended from the sides of an anterior division of the trunk, 

 and the branchiae (d,) are placed, as in the doris, on the pos- 

 terior part of the back, but at a distance from the anus, which 

 here opens on the anterior part of the right side, as in the 

 clio. The muscular arms are comparatively large in the 

 small testaceous cleodora, (Fig. 6'7- C. b,) as they are also in 

 the testaceous cymbulia, represented in Fig. 24. The fleshy 

 mantle of the cleodora extends laterally to a distance from 

 the sides of the head (,) and the slender pellucid, depressed, 

 tapering shell (c,) is also expanded transversely with deeply 

 grooved sides. The fins for progressive motion are more 

 lengthened and straight in their form in the minute testa- 

 ceous cuvieria (Fig. 6J . D. a,) where there are dentiform 

 masticating buccal organs, as in a cephalopod, and in which 

 the shell (c,) is straight, lengthened, conical, and pointed, 

 like a belemnite. The muscular organs of these and the 

 other known forms of pteropods, are constructed, like their 

 shells, on the plan of those of the cephalopods, especially of 

 the lower forms of that class. 



The organs of motion in the cephalopods, as in the ptero- 

 pods, are generally in form of muscular fins extending from 

 the sides of the trunk, and unsupported by osseous rays ; 

 they move also by means of the muscular feet developed 

 from the fleshy disk surrounding the head. The nautilus, 

 like a gasteropod, is fixed by two lateral muscles to the bot- 

 tom of its shell, its muscular open mantle is thin and deli- 

 cate, the muscular funnel is open beneath throughout its 

 whole length, and the mouth, surrounded with strong mus- 



