| arch of the aorta | The curved portion between the ascending and descending parts of the aorta; it begins as a continuation of the ascending aorta posterior to the sternal angle, runs posteriorly and slightly to the left as it passes over the root of the left lung, and becomes the descending aorta as it reaches and begins to course along the vertebral column; it gives rise to the brachiocephalic trunk, the left common carotid and left subclavian arteries. Any member of the several pairs of arterial channels encircling the embryonic pharynx in the mesenchyme of the brachial arches; there are potentially six pairs, but in mammals the fifth pair is poorly developed or absent. The first and second pairs are functional only in very young embryos; the third pair is involved in the formation of the carotids; the fourth arch on the left is incorporated in the arch of the aorta; the sixth pair forms the proximal part of the pulmonary arteries. A series of arterial channels encircling the embryonic pharynx in the mesenchyme of the branchial arch's. There are potentially six pairs, but in mammals the fifth pair is poorly developed or absent. The first and second pairs are functional only in very young embryos; the third pair is involved in the formation of the carotids; the fourth arch on the left is incorporated in the arch of the aorta; the sixth pair forms the proximal part of the pulmonary arteries. Synonym: arcus aortae. (05 Mar 2000) |
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| arch of the palate | The vaulted roof of the mouth. (05 Mar 2000) |
| arch of thoracic duct | See: thoracic duct. (05 Mar 2000) |
| arterial arch of lower eyelid | Formed by the medial palpebral artery which communicates with a branch of the lacrimal artery along the tarsal margin. Synonym: arcus palpebralis inferior. (05 Mar 2000) |
| arterial arch of upper eyelid | Formed by communicating branches of the medial and lateral palpebral arteries. Often two arches are present, one located near the free border of the tarsal plate, the other along the upper border of the tarsus. Synonym: arcus palpebralis superior. (05 Mar 2000) |
| available arch length | <dentistry> The amount of space available for the permanent teeth around the dental arch from the first permanent molar on the left to the first permanent molar on the right. (05 Mar 2000) |
| axillary arch | <anatomy> An anomalous muscle or tendinus slip that passes across the axilla from the pectoralis major to insert with the latissimus dorsi onto the humerus. Though to be a vestige of the panniculus carnosus muscle of lower mammals. Synonym: axillary arch muscle, axillary arch, pectorodorsal muscle. (05 Mar 2000) |
| axillary arch muscle | <anatomy> An anomalous muscle or tendinus slip that passes across the axilla from the pectoralis major to insert with the latissimus dorsi onto the humerus. Though to be a vestige of the panniculus carnosus muscle of lower mammals. Synonym: axillary arch muscle, axillary arch, pectorodorsal muscle. (05 Mar 2000) |
| Byzantine arch palate | Incomplete fusion of the palatal process with the nasal spine. (05 Mar 2000) |
| palatoglossal arch | One of a pair of ridges or folds of mucous membrane passing from the soft palate to the side of the tongue; it encloses the palatoglossus muscle and forms anterior margin of the tonsillar fossa. Also demarcates oral cavity from isthmus of fauces. Synonym: arcus palatoglossus, anterior palatine arch, anterior pillar of fauces, arcus glossopalatinus, glossopalatine arch, glossopalatine fold. (05 Mar 2000) |
| palatopharyngeal arch | One of a pair of ridges or folds of mucous membrane which passes downward from the posterior margin of the soft palate to the lateral wall of the pharynx. It encloses the palatopharyngeus muscle and forms the posterior margin of the tonsillar fossa. It also demarcates the isthmus of fauces from oropharynx. Synonym: arcus palatopharyngeus, pharyngopalatine arch, posterior palatine arch, posterior pillar of fauces. (05 Mar 2000) |
| malar arch | The arch formed by the temporal process of the zygomatic bone that joins the zygomatic process of the temporal bone. Synonym: arcus zygomaticus, cheek bone, malar arch, zygoma. (05 Mar 2000) |
| mandibular arch | The first postoral arch in the branchial arch series. Synonym: mandibular process. (05 Mar 2000) |
| vertebral arch | The posterior projection from the body of a vertebra that encloses the vertebral foramen; it consists of paired pedicles and laminae; the spinous, transverse, and articular processes arise from the arch. In aggregate, the venous arches-and the ligamenta flava that unite them-form the posterior wall of the vertebral (spinal) canal. Synonym: arcus vertebrae, neural arch. (05 Mar 2000) |
| gill arch skeleton | Cartilages associated with the visceral portion of the embryonic mammalian chondrocranium, representing the gill arch (branchial) skeletons as seen in shark-type fishes; they are the primordia of Meckel's cartilage, the styloid, hyoid, cricoid, thyroid, and arytenoid cartilages, and the auditory ossicles. See: branchial arches. (05 Mar 2000) |