. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. Fig. 47.—Pectoral Akch op PAtasoHAT- TERiA (from the ventral side) After Credner. 8, scapula ; O, coracoid ; d, clavicle ; episternun. SlJS, lu the StegocejAala, the episternum (" interclavicle ") consists of a large bony plate, situated ventrally to the sternum, some of the various forms of which, as "well as its relation to the pectoral arch and more particularly to the clavi- cles, will be seen by refer- ence to Fig. 46. The episternum of Palceohatteria and of re- cent Lizards and Crocodiles is essent
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. Fig. 47.—Pectoral Akch op PAtasoHAT- TERiA (from the ventral side) After Credner. 8, scapula ; O, coracoid ; d, clavicle ; episternun. SlJS, lu the StegocejAala, the episternum (" interclavicle ") consists of a large bony plate, situated ventrally to the sternum, some of the various forms of which, as "well as its relation to the pectoral arch and more particularly to the clavi- cles, will be seen by refer- ence to Fig. 46. The episternum of Palceohatteria and of re- cent Lizards and Crocodiles is essentially similar to that of the Stegocephala (Figs. 44, 46, and 47). In Lacerta ar^d Crocodilus it arises, from before back- wards, as a paired structure,, which is not preformed in cartilage. An epistermim is wanting in Chelonia and Ophidia, as well as in Chamseleo and Anguis. In Birds no independent elements corresponding to this structure can be recognised; the ligament extending between the clavicles and the sternal keel, the periosteal covering of the keel which is continued -backward from this ligament, and the median portion of the fused clavicles when separately ossified ("interclavicle") may possibly have something to do with an episternum without being exactly homologous with it. The origin and meaning of the mammalian episternum, which is pre- formed in cartilage, is not known; it has probably no direct connection with the similarly-named structure in Keptiles, but apparently agrees with the latter at any rate as regards position and relations in the embryo Mole (Fig. 47a). In Monoiremcs (Fig. 48) and certain Marsupials a median and two lateral portions can be distinguished, the latter being in connection with the clavicles. In these Marsupials the median portion unites with the ster- num, and as in Monotremes, becomes. Fig. Ha.—Episternum of an Embryo Mole. (After A. Giitte). St, sternum ; es^, central por- tion and es", lateral por- tion of the epis
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
