. Chordate morphology. Morphology (Animals); Chordata. left and right brachiocephalic fused MAMMAL HUMAN C CAT Q HEDGEHOG E OX ORNIiHORHYNCHUS KANGAROO WOMBAT Figure 11-10. Variations in the arterial roots of mammals. (After Romer, 1955, and Owen, 1868} odile, but this has not been observed. The loss of this arch results in the functional separation of pulmonary and sys- temic circulations in the bird, a parallelism to that observed in the mammal. As a result of the elongation of the neck and the posterior displacement of the heart, relationships between the carotids are altered. In the foetus
. Chordate morphology. Morphology (Animals); Chordata. left and right brachiocephalic fused MAMMAL HUMAN C CAT Q HEDGEHOG E OX ORNIiHORHYNCHUS KANGAROO WOMBAT Figure 11-10. Variations in the arterial roots of mammals. (After Romer, 1955, and Owen, 1868} odile, but this has not been observed. The loss of this arch results in the functional separation of pulmonary and sys- temic circulations in the bird, a parallelism to that observed in the mammal. As a result of the elongation of the neck and the posterior displacement of the heart, relationships between the carotids are altered. In the foetus of 6 to 7 days, a commissure con- nects the external and internal carotids near the head, and the external carotid stem may lose connection with its cranial extreme. The stem is now called the ascending esophageal or superficial cervical. The internal carotids come to lie next to each other at the midline in a hypophyseal canal. In some the carotids fuse, and the left or right root for this common vessel may be the larger. In other species, only the left carotid is re- tained. The variations of the carotids were used by Garrod (1873) in the classification of birds. The changes observed in the bird parallel those in the crocodilian in which only the left carotid is retained and the external carotid stems (collateralis colli) maintain their distal connections. The posterior displacement of the heart is also reflected in the subclavian arteries. The subclavian arises as a seg- mental artery from the dorsal aorta posterior to the pharyn- geal region. About the sixth day the heart is moved back in relation to the limb; a new subclavian stem develops from the external carotid region (ventral radix aortae) of carotid systemic arcl subclavian (pri internal carotid external carotid. Imona. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resembl
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Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
