ANATOMY OF THE TEREBRATIJLA. 7 



anterior and posterior portion ; glides between the stomach and the crus of the calcareous 

 loop of its own side, and is attached by the double expanded insertion into the dorsal or 

 perforated valve, d : for the anterior division, I propose the name of ' adductor longus 

 anticus,' o, for the posterior one, that of ' adductor longus posticus,' p ; but both of the so- 

 divided adductors, by reason of their ventral confluent attachment, may be regarded as 

 constituting one quadricipital muscle. The action of this complex muscle is directly to 

 close or adduct the valves, in which action it will slightly compress the hepatic lobes and 

 stomach. 



The adductor hrevis, ib. q, forms a symmetrical pair, having their expanded disc of attach- 

 ment to the ventral valve extended somewhat in advance of the confluent insertion of the 

 preceding muscles : the fibres of each pass obliquely backwards, and converge to a small 

 round shining tendon, the tendons passing on each side the intestine to be inserted close 

 together into the cardinal process of the dorsal valve, d. Their action will be to adduct the 

 valves ; but with a more oblique movement bearing upon the ventral valve, v, which 

 they, as it were, help to suspend from the hinge, as from a fixed point. 



A third pair of carneo- aponeurotic muscles, u, which pass from valve to valve, are 

 attached by both extremities nearer their line of junction, serve to strengthen the hinge, 

 and, by compressing the sides of the base of the peduncle, may aid in protruding that 

 part after it has been forcibly retracted : the muscles in question, which I propose to call 

 ' musculi cardinales' or hinge muscles, are attached by their smaller and most tendinous 

 extremity to the linear ridge between the hinge-teeth cavities, fig. 1, p. 9, h, and hinge- 

 plate, ib. c, 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 attach- 

 ment 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 

 compressors and elongators, or protrusors, of the peduncle. 



The name retractor inferior, pi. i, fig. 2, s, 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 backwards, 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 perforated valve to the peduncle, and forms the most direct 

 retractor of that part, and consequently the chief agent in such limited movements, as the 

 fettered state of the shell will allow. 



The name * retractor superior,' ib. t, 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, ib, fig. 2>, t, t : the fibres curve over the sides of 



