. Chordate morphology. Morphology (Animals); Chordata. anterior cerebral artery_ anterior circle of Willis middle cerebroL posterior communicating ophthalmic artery nternol carotid superior cerebellar palatine arteries bosilor artery, ertebral artery anterior inferior cerebellar posterior inferior cerebellar- — middle cerebral ~ ophthalmic artery moxillory ortery, internal carotid lingual. vertebral artery external carotid thyroid common carotid stem brachiocephalic pulmonary artery, subclavian artery radix oortoe. internal mommory ductus arteriosus dorsal aorta Figure 11-26. Three stages of a
. Chordate morphology. Morphology (Animals); Chordata. anterior cerebral artery_ anterior circle of Willis middle cerebroL posterior communicating ophthalmic artery nternol carotid superior cerebellar palatine arteries bosilor artery, ertebral artery anterior inferior cerebellar posterior inferior cerebellar- — middle cerebral ~ ophthalmic artery moxillory ortery, internal carotid lingual. vertebral artery external carotid thyroid common carotid stem brachiocephalic pulmonary artery, subclavian artery radix oortoe. internal mommory ductus arteriosus dorsal aorta Figure 11-26. Three stages of anterior arterial development in man. (After Patten, 1946) the circle of Willis; these join the internal carotids. The an- terior cerebrals now appear, and there is a small communi- cating branch between them which completes the anterior half of the circle of Willis. The anterior cerebrals extend forward and upward on the inner surface of the two cere- bral lobes. The spinal artery arises as a posterior midline develop- ment from the basilar artery, and it extends back inside of the vertebral canal. The ophthalmic artery arises as a branch of the internal carotid just before it is joined by the poste- rior communicating division of the basilar artery. Meanwhile the external carotid, the anterior extension of each of the paired ventral aortae, has given rise to the ex- ternal maxillary, the lingual, and the thyroid arteries. RepHles In the reptile (Figure 11-27) the external carotid is represented by the lingual (or mental) branch of the com- mon carotid. The carotid stem branches to form the inter- nal carotid and the stapedial artery. The internal carotid passes ventromedially into the parabasal canal. Here it gives rise to a palatine artery, which emerges above the palatine bone, then enters the sella to supply the middle and ante- rior cerebral arteries. In Sphenodon a parabasal canal is lacking; the palatine branch arises before the internal ca- rotid enters the basis cran
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