488 LECTURE XX. 



(v), which they, as it were, help to suspend from the hinge,'as from a 

 fixed point. 



A third pair of carneo-aponeurotic muscles (h), which pass from 

 valve to valve, have both extremities nearer the hinge, and, by com- 

 pressing the sides of the base of the peduncle, may aid in protruding 

 that part after it has been forcibly retracted : these " musculi cardi- 

 nales,'^ or hinge-muscles, are attached by their smaller and most 

 tendinous extremity to the linear ridge between the hinge-teeth 

 cavities and hinge plate in the imperforate valve. They arise by 

 their larger and more fleshy ends from the imperforate valve, close 

 together, behind the common attachment of the adductores longi, the 

 rectum alone intervening ; some of their fibres appear to be lost upon 

 the sides of the sheath of the peduncle. The proper muscles of the 

 peduncle consist of two pairs, for its retraction and attachment to the 

 valves ; and of some circular or transverse fibres of the sheath, 

 which, though for the most part of an aponeurotic character, appear 

 to be arranged so as to act as compressoi's and elongators, or pro- 

 trusors, of the peduncle. 



The name retractor inferior (k) is given to a pair of muscles which 

 arise from the ventral valve by a thick carneous end, exterior to the 

 "adductores longi "and "brevis;" the fibres pass obliquely back- 

 wards, and rapidly diminish to a tendon which penetrates the upper 

 and lateral part of the sheath of the peduncle, and the terminal fibres 

 of which appear to constitute part of the peduncle itself. This pair 

 of muscles serves to suspend the Terebratula by means of the perfo- 

 rated vaWe to the peduncle, and forms the most direct retractor of 

 that part, and consequently the chief agent in such limited move- 

 ments, as the fettered state of the shell will allow. 



The name " retractor superior " (i) is applied to a pair of muscles 

 which have a broad subtriangular carneous origin from the hinge- 

 plate, and a strong aponeurosis extending therefrom to the crus of 

 the calcareous loop (a) ; the fibres curve over the sides of the swollen 

 part of the capsule of the peduncle (I), penetrate the capsule, interlace 

 with the inserted fibres of the inferior retractor, and terminate for 

 the most part in the peduncle. 



Some not vei-y clearly defined, partly carneous, chiefly tendinous* 

 fibres, which interlace, running mostly in the transverse direction 

 upon and in the capsule of the peduncle, and make up, in fact, a chief 

 part of its substance, have a transversely oblong surface of attach- 

 ment or strong adhesion to the lower part of the bent conical pro- 

 longation of the ventral valve lodging the peduncle : this surface 

 appears in the exterior of the soft parts of the Terebratula, behind 



