![]() These thin, broad muscles squeeze the pharynx closed as part of the pumping action necessary for gill breathing. Some of the deeper fibres attach to the gill bar and may run between adjacent bars. Most fibres attach, dorsally and ventrally, to connective tissues (fascia) that sheath the body. Superficially, a thin sheet comprising dorsal and ventral constrictor muscles runs in the flap of skin that covers each gill slit and forms the gill septum. Each cartilaginous arch is provided with a set of branchial muscles that receives separate, visceral innervation. The cartilages are arranged at angles to each other. Each arch has a visceral skeleton comprising five cartilages named, from dorsal to ventral, the pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, and basibranchial. The posterior five gill arches of more primitive sharks, however, are a good model for the condition in the ancestral jawless fishes. The sharks and other cartilaginous fishes (the class Chondrichthyes) have modified the structure of the first two arches the cartilages of the anterior arch form the mandible and upper jaw (palatoquadrate), and modifications also have taken place in the second, hyoid arch. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians. ![]() COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.From tech to household and wellness products. Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |