. Elements of Comparative Anatomy. 588 COMPAEATIVE AN'ATOMY. There are various kinds of modifications in the Mammalia, wliich. are due to similar changes in the vascular trunk during em- bryonic life. Among others these specially affect the ter- minal branches of the carotids; the internal carotid, as in various Lizards and Birds, is not sent to the cranial cavity and sensory organs only. The arteries of the fore- limbs arise from various and very different points, so that transmission appears to be of less importance than adapta- tion in the development of these vessels. The trunk of the aort
. Elements of Comparative Anatomy. 588 COMPAEATIVE AN'ATOMY. There are various kinds of modifications in the Mammalia, wliich. are due to similar changes in the vascular trunk during em- bryonic life. Among others these specially affect the ter- minal branches of the carotids; the internal carotid, as in various Lizards and Birds, is not sent to the cranial cavity and sensory organs only. The arteries of the fore- limbs arise from various and very different points, so that transmission appears to be of less importance than adapta- tion in the development of these vessels. The trunk of the aorta is continued along the vertebral column, without any change in character, as far as the por- tion ^vhich is set apart for the caudal region—caudal artery; when the tail is shortened, it forms the median sacral artery. When the so-called chevron bones are present, the terminal portion of the aorta always lies in the canal formed by them. But in various Fishes it may be enclosed in a canal, formed by processes from the centra of the vertebrte, in the region of the trunk also ; this is the case in the Sturgeon, and in some Teleostei. The aorta gives off arteries (arteriee intercostales) for the metameres in regular succes- sion, as well as the vessels which go to the viscera, and also those which go to the hind- limbs, when these are well developed. In Fishes there is ordinarily only one large arterial trunk for the viscera (A. coeliaco-mesenterica); but in some there is a mesenteric artery also. The aorta gives off a larger number of arteries for the renal and generative organs. As. Fig. 333. Heart aiiil groafc vessels of Bnteo vulgaris, tr Trachea, i Crop, ae Com- munication between the air-sacs and the lungs. h Bursa Fabricii. ao Aortic arch. aad Art. anonyma dextra. aas Art. anonyma sinistra. ^s Art. pulmonalis sinistra. c Carotid. am Visceral artery, vci Com- mencement of the inferior vena cava. van Vena Please note that these images are extracted f
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