. Elements of Comparative Anatomy. 586 COMPAEATIVE ANATOMY. arterial circulus ceplaalicus at the base of the skull. A special optic artery is given, off from the vessels of the rudimentary gill, with which a direct branch of the first branchial vein (Selachii), or a branch of the same vessel which surrounds the body of the hyoid (Teleostei), is connected. There are numerous modifications in the mode of origin and arrangement of the different vessels, the most important of which are found in the carotid and optic arteries. This portion of the vascular system is arranged in a similar manner in t
. Elements of Comparative Anatomy. 586 COMPAEATIVE ANATOMY. arterial circulus ceplaalicus at the base of the skull. A special optic artery is given, off from the vessels of the rudimentary gill, with which a direct branch of the first branchial vein (Selachii), or a branch of the same vessel which surrounds the body of the hyoid (Teleostei), is connected. There are numerous modifications in the mode of origin and arrangement of the different vessels, the most important of which are found in the carotid and optic arteries. This portion of the vascular system is arranged in a similar manner in the Amphibia. In the Perennibranchiata the cephalic arteries arise from the anterior portion of the roots of the aorta; in the Caducibranchiata, from the first permanent aortic arch, or, they are continuations of the anterior arch itself (Fig. 331, c). In this case, an artery which goes to the tongue {I) represents an external carotid. After this vessel is given off, there is a swelling (c) on the carotid trunk in the Frogs and in the Sala- manders ; this is the so-called carotid gland. The lumen of the vessel is here traversed by a network of bands, which break it up into a number of narrower passages, just as if a capillary network had been intercalated in the course of an artery. The carotid gland appears to be de- rived from an arrangement of this kind, the branchial vascular network not having been com- pletely ati'ophied. The next pair form the aortic arches {ad as), which converge backwards, and finally unite into an unpaired aortic trunk {a). Each aortic arch gives off a subclavian {sd ss). Just before they unite, a large visceral artery (m) is given off from the left aorta. The pulmonary artery represents a last aortic arch. Before it goes to the lungs (^:>) it gives off a large cutaneous branch (cut), which ramifies on the back and neck as far as the posterior region of the head, and affords a distinct proof of the respiratory function of the integument. In the earl
Size: 1282px × 1950px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1870, bookpublisherlondonmacmillan
