The visceral arches are seven in number. The first or _mandibular arch_ consists on each side of an upper portion, the _palato-pterygo-quadrate_ or _palato-quadrate_ cartilage, which passes forwards in the side-wall of the oral cavity, along the upper margin of the mouth, its anterior or palatine part curving inwards to a ligamentous connexion with its fellow beneath the cranial floor. Each cartilage has an upwardly directed process (_ethmo-palatine process_) which is connected by a suspensory _ethmo-palatine ligament_ with the lateral wall of the cranium behind the lateral ethmoid process. The lower or ventral half of the mandibular arch (_Meckel's cartilage_) is similar in shape to the upper; it articulates behind with the quadrate portion of the latter by a movable joint, and is thence prolonged forwards and downwards in relation with the lower margin of the mouth to a median ligamentous union with its fellow of the opposite side. The palato-pterygo-quadrate and Meckel's cartilages together form the primitive upper and lower jaws, and support the teeth. The _hyoid arch_ also consists of a dorsal and a ventral half on each side. The dorsal half or _hyomandibular_ element articulates above with the periotic capsule. The ventral portion, or _cerato-hyal_, passes downwards and is connected with its fellow by a median copula or _basi-hyal_ cartilage situated in the floor of the oral cavity. A series of simple cartilaginous rays (_branchial rays_) are attached to the hinder margins of the hyomandibular and cerato-hyal elements. The distal end of the hyomandibular is connected by strong ligaments with the hinder portions of both the palato-pterygo-quadrate cartilage and Meckel's cartilage; in fact, {210}the hyomandibular is the effective suspensorium by which the upper and lower jaws are connected with the skull, and all Fishes in which this arrangement exists are said to be _hyostylic_.[189] Behind the hyoid arch follow five _branchial arches_. Each of these is segmented into a dorsal or _pharyngo-branchial_ element, followed by an _epi-_, a _cerato-_, and a _hypo-branchial_ piece, but the later element is absent in the fifth arch. The lateral halves of the last three arches are connected ventrally by a large median basi-branchial cartilage, but in the first and second arches by the median apposition of their respective hypo-branchial elements. Like the hyomandibular and cerato-hyal segments of the hyoid arch, the epi- and cerato-branchial elements of all the branchial arches except the fifth are fringed along their outer convex margins by a series of _branchial rays_, and, in addition, there are three pairs of slender, curved, cartilaginous rods, or _extra-branchials_, in relation with the distal extremities of the branchial rays of the second, third, and fourth branchial arches. The function of the branchial arches, and their branchial rays, and extra-branchial cartilages, is to support the inter-branchial septa which