Bardskull

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Hearing and vision are the most highly developed avian senses, and the position of the ears and eyes in the skull plays a big role in the way birds perceive the world. How structures in bodies develop in the embryos have often been found to reflect how those structures changed during evolution. Embryonic humans at early stages, for example, look a lot like embryonic fish, and later in development as embryos of other mammals, betraying our origins on the evolutionary tree. The bird brain is divided into a number of sections, each with a different function. The cerebrum or telencephalon is divided into two hemispheres, and controls higher functions. The telencephalon is dominated by a large pallium, which corresponds to the mammalian cerebral cortex and is responsible for the cognitive functions of birds. The pallium is made up of several major structures: the hyperpallium, a dorsal bulge of the pallium found only in birds, as well as the nidopallium, mesopallium, and archipallium. The bird telencephalon nuclear structure, wherein neurons are distributed in three-dimensionally arranged clusters, with no large-scale separation of white matter and grey matter, though there exist layer-like and column-like connections. Structures in the pallium are associated with perception, learning, and cognition. Beneath the pallium are the two components of the subpallium, the striatum and pallidum. The subpallium connects different parts of the telencephalon and plays major roles in a number of critical behaviours. To the rear of the telencephalon are the thalamus, midbrain, and cerebellum. The hindbrain connects the rest of the brain to the spinal cord. The avian stomach is composed of two organs, the proventriculus and the gizzard that work together during digestion. The proventriculus is a rod shaped tube, which is found between the esophagus and the gizzard, that secretes hydrochloric acid and pepsinogen into the digestive tract. [65] The acid converts the inactive pepsinogen into the active proteolytic enzyme, pepsin, which breaks down specific peptide bonds found in proteins, to produce a set of peptides, which are amino acid chains that are shorter than the original dietary protein. [66] [67] The gastric juices (hydrochloric acid and pepsinogen) are mixed with the stomach contents through the muscular contractions of the gizzard. [68] Gizzard [ edit ] Dr Abzhanov said: “Evolution is the accumulation of and selection on changes made to the developmental process. Studying birds is a fascinating subject because they retain features of ‘young’ dinosaur ancestors, while also clearly adding their own adaptations, such as toothless beaks and wings.

Air passes unidirectionally through the lungs during both exhalation and inspiration, causing, except for the oxygen-poor dead space air left in the trachea after exhalation and breathed in at the beginning of inhalation, little to no mixing of new oxygen-rich air with spent oxygen-poor air (as occurs in mammalian lungs), changing only (from oxygen-rich to oxygen-poor) as it moves (unidirectionally) through the parabronchi. By comparing brains and skulls in both ancient fossils and throughout the early life of modern reptiles, the team were able to use the same analytical approach to look at both evolutionary and developmental aspects of brain-skull interactions.Although this general rule still stands, since that time, observations have been made of a few exceptions in both directions. [72] [74] Birds have a large brain to body mass ratio. This is reflected in the advanced and complex bird intelligence. a b c d Bhullar, Bhart-Anjan S.; Hanson, Michael; Fabbri, Matteo; Pritchard, Adam; Bever, Gabe S.; Hoffman, Eva (2016-09-01). "How to Make a Bird Skull: Major Transitions in the Evolution of the Avian Cranium, Paedomorphosis, and the Beak as a Surrogate Hand". Integrative and Comparative Biology. 56 (3): 389–403. doi: 10.1093/icb/icw069. ISSN 1540-7063. PMID 27371392.

Stryer, Lubert (1995). In: Biochemistry (4thed.). New York: W.H. Freeman. pp.250–1. ISBN 0-7167-2009-4. Herrera, A. M; Shuster, S. G.; Perriton, C. L.; Cohn, M. J. (2013). "Developmental Basis of Phallus Reduction during Bird Evolution". Current Biology. 23 (12): 1065–74. doi: 10.1016/j.cub.2013.04.062. PMID 23746636. Du Brul, E. Lloyd (1962). "The general phenomenon of bipedalism". American Zoologist. 2 (2): 205–208. doi: 10.1093/icb/2.2.205. Kinesis of the cranium of a macaw with upper mandible lowered (left), with upper mandible raised (centre), and with forces acting upon the mandible (right). (more)Simonetta, Alberto M. (1960-09-01). "On the Mechanical Implications of the Avian Skull and Their Bearing on the Evolution and Classification of Birds". The Quarterly Review of Biology. 35 (3): 206–220. doi: 10.1086/403106. ISSN 0033-5770. S2CID 85091693. DÜZLER, A.; ÖZGEL, Ö.; DURSUN, N. (2006). "Morphometric analysis of the sternum in avian species" (PDF). Turkish Journal of Veterinary and Animal Sciences. 30: 311–314. ISSN 1303-6181. Archived from the original (PDF) on 2013-11-12 . Retrieved 2013-03-01. The bones of the forelimb are modified for flight with feathers. Major modifications include restriction of the motion of the elbow and wrist joints to one plane, reduction of the number of digits, loss of functional claws, fusion of certain bones of the “hand” (the metacarpals and most of the carpals) into a carpometacarpus, and modification of the elements, especially those toward the tip of the limb (distal), for the attachment of feathers. The wing bones are hollow, and the cavity in the humerus is connected with the air-sac system. As a general rule, large flying birds have proportionally greater pneumaticity in the skeleton than small ones. The highly pneumatic bones of large flying birds are reinforced with bony struts at points of stress. The humerus, radius, and ulna are well developed. The secondary flight feathers are attached to the ulna, which thus directly transmits force from the flight muscles to these feathers and is therefore relatively heavier than the radius. Two small wrist bones are present: the radiale, or scapholunar, and the ulnare, or cuneiform. The former lies between the distal end of the radius and the proximal part (the part toward the body) of the carpometacarpus. When the elbow joint is flexed (bent), the radius slides forward on the ulna and pushes the radiale against the carpometacarpus, which in turn flexes the wrist. Thus the two joints operate simultaneously. The U-shaped ulnare articulates with the ulna and the carpometacarpus. Anatomists differ on which bones of the reptilian “hand” are represented in the bird’s wing. Embryological evidence suggests that the digits are II, III, and IV, but it is possible that they are actually I, II, and III. The carpometacarpus consists of fused carpals (bones of the wrist) and metacarpals (bones of the palm), metacarpals II and III (or III and IV) contributing the greater part of the bone. The bones of the “fingers” (phalanges) are reduced to one each on the outer and inner digits and two on the middle one. The primary flight feathers are attached to the carpometacarpus and digits, the number attached to each being characteristic of the various major groups of birds.