A manual of the anatomy of vertebrated animals / by Thomas H. Huxley.

Date:
1871
Catalogue details

Licence: Public Domain Mark

Credit: A manual of the anatomy of vertebrated animals / by Thomas H. Huxley. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    no brancliial filaments, but commonly support teeth, and are called hypojoharyngeal bones. In certain osseous fishes, thence called Fharyngognatld, they ankylose together into one bone. The anterior four pair are composed of several joints, and the uppermost articulations of more or fewer of them usually expand, bear teeth, and form the epipharyngeal bones. Sundry important membrane bones are connected with the mandibular and hyoidean arches. The preoper- culum {P.Op.), operculum {Op.), and hranchiostegal rays (Br.), already met with among the Ganoidei, are the most constant of these. Beneath the operculum, lies a suhoperculum (S.Op.), and below this an interoperculum (I.Op.), which is con- nected by ligament with the angular piece of the lower jaw, and is also united to the outer face of the hyoidean arch. It may be altogether ligamentous, as in the Siluroids. The hranchiostegal rays are attached partly to the inner, and partly to the outer, surface of the hyoidean arch. They support a membrane, the hranchiostegal membrane, which serves as a sort of inner gill-cover. Most Teleodei possess two pair of limbs, the pectoral and the ventral fins. But the latter are often absent, and the former are occasionally wanting. When the pectoral fins are absent, the pectoral arch usually remains, though it may be reduced to little more than a filament, as in Murcen- ophis. The ventral fins are frequently situated in their nor- mal position beneath the posterior part of the trunk; but in considerable groups of these fishes they are immediately behind the pectoral fins {thoracic), or even in front of them {jugular). In the asymmetrical Pleuronectidce one pectoral fin may be larger than the other, or may alone remain, as in Monochirus. The pectoral arch always consists of a primarily cartila- ginous coraco-scapular portion—which usually ossifies in two pieces, a coracoid below, and a scapula above—and of sundry membrane bones. The chief of these membrane bones is the clavicula {CI.), which meets its fellow in the middle line, and is usually joined to it by ligament, but sometimes, as