Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 588 COMPARATIVE ANATOMY. There are various kinds of modifications in the Mammalia, which 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 ada
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 588 COMPARATIVE ANATOMY. There are various kinds of modifications in the Mammalia, which 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 which 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 vertebras, in the region of the trunk also ; this is the case in the Sturgeon, and in some Teleostei. The aorta gives off arteries (arteriso 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. cceliaco-mesenterica); but in some there is a mesenteric artery also. The aorta gives off a larg-er number of arteries for the renal and generative organs. As Fig. 333. Heart and great vessels of Buteo vulgaris, tr Trachea, i Crop, ae Com- munication between the air-sacs and the lungs. b Bursa Fabricii. ao Aortic arch. aad Art. anonyma dextra. aas Art. anonyma sinistra. ps Art. pulmonalis sinistra, c Carotid. am Visceral artery. vci Com- mencement of the inferior vena cava. vcm Vena
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