Text-book of comparative anatomy . s stretched between the invaginated wall of the proboscissheath and the neighbouring outer body wall (parieto-vaginal muscles) ; (3) ofcircular muscles, generally developed only on the anterior body wall, though inPaludicella they appear as subdermal muscular hoops in the whole body, and bytheir contraction cause the protrusion out of the cells of the withdrawn anteriorend of the body with its tentacles. All these circular muscles are to be consideredas remains of the circular muscle layer; the retractors and parieto-vaginal muscles asremains of the longitudi
Text-book of comparative anatomy . s stretched between the invaginated wall of the proboscissheath and the neighbouring outer body wall (parieto-vaginal muscles) ; (3) ofcircular muscles, generally developed only on the anterior body wall, though inPaludicella they appear as subdermal muscular hoops in the whole body, and bytheir contraction cause the protrusion out of the cells of the withdrawn anteriorend of the body with its tentacles. All these circular muscles are to be consideredas remains of the circular muscle layer; the retractors and parieto-vaginal muscles asremains of the longitudinal musculature of a dermo-muscular tube. Iii the Brachiopoda a typical dermo-muscular tube is as littledeveloped as in the Bryosoa; its absence is here also evidently tobe referred to the development of a shell. As remains of a dermo-muscular tube, there are: (1) lying under the integument of themantle, weakly-developed fibres running transversely and longitu-dinally ; (2) the arm muscles (protractors and retractors); and (3) the. UD FIG. 129.—Preparation of Waldheimia flavescens (after Owen), seen from the right side, todemonstrate the musculature, the peduncle (p) and the calcareous framework (D) which servesto support the arms. Dd, Dorsal, Dv, ventral shell valve ; TOJ, M2> ms> m4> muscles for opening andclosing the shell. longitudinal muscles of the peduncle, which, in the almost universalabsence of a circular musculature, are counteracted by its elastic the Brachiopoda a system of strong dorso-ventral musclespassing through the body cavity (Fig. 129) serve for closing andopening the two valves of the shell (adductors and divaricators). Theyare attached to both the shell valves in the posterior region of thebody in the neighbourhood of the hinge (where this is present).These muscles cannot be regarded as dislocated or modified portions ofthe dermo-muscular tube. In Dinophilus there is found under the body epithelium a veryweakly developed dermo-muscular
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
