Text-book of comparative anatomy . As a varying number of the anterior thoracic segments may fuse with the head,a varying number of the anterior thoracic feet often enter into close relations withthe mouth, as accessory organs for the taking in of food (foot-jaws, maxillipedes).The thoracic foot of Ncbalia described above may be considered as the primitiveform of the thoracic feet in the Malacostraca. In a typical Malacostracan thoracic limb the proximal joint of the protopodite 318 COMPARA Tl 1 rE AX A TOMY CHAP. carries an epipodite, while the exopodite and the 5-jointed endopodite are attac
Text-book of comparative anatomy . As a varying number of the anterior thoracic segments may fuse with the head,a varying number of the anterior thoracic feet often enter into close relations withthe mouth, as accessory organs for the taking in of food (foot-jaws, maxillipedes).The thoracic foot of Ncbalia described above may be considered as the primitiveform of the thoracic feet in the Malacostraca. In a typical Malacostracan thoracic limb the proximal joint of the protopodite 318 COMPARA Tl 1 rE AX A TOMY CHAP. carries an epipodite, while the exopodite and the 5-jointed endopodite are attachedto the distal joint. Very often both the exopodite and the epipodite disappear, andthe thoracic foot is then an unbranched, 7-jointed limb. The proximal joint of theprotopodite occasionally fusing with the skeleton of the thorax, the distal joint aloneis recognisable. Arthrostraca (Fig. 217).—Here, where the most anterior thoracic segment isfused with the head, the most anterior pair of thoracic feet are associated with the. FIG. 217.—Thoracic limbs of some Arthrostraca. A, 1st pair of thoracic feet (maxillipedes) ofAmphithoe penicillata (Costa). B-D, Apseudes. B, 1st right thoracic foot; C, 3d thoracic foot;D, 2d thoracic foot (after Boas). E and F, Asellus. E, 3d thoracic foot; F, 1st thoracic foot (afterBoas). I, II, Joints of the protopodite ; 1-5 joints of the endopodite ; 7;, ki, masticatory ridges ; ep,epipodite ; ex, exopodite ; en, endopodite. oral limbs as a pair of maxillipedes. The absence of the exopodite is the generalrule for the thoracic feet of the Arthrostraca. The proximal joint of the protopoditeoften fuses with the thoracic skeleton. On the basal joint of some thoracic feetthere is, in the female, a lamellate appendage, the brood plate or lamella. The brood plates cover over a cavity, the brood pouch,on the ventral side of the thorax, and intothis pouch the eggs enter and there develop(Fig. 218). The first thoracic foot (niaxillipecle) ischaracterise
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
