6 NATURAL HISTORY. 



the tympanic pedicle. At their anterior corners are the pre-frontal bones, which defend and support 

 the olfactory prolongation of the brain, and form the front border of the orbit. On the base of 

 the skull, wedged into the para-sphenoid, is the vomer ; its upper surface supports the nasal bones. 

 In the genus Lepidosteus it is divided longitudinally into two. In. many fishes the vomer carries teeth. 

 The pre-frontals and nasals are both sometimes blended with the vomer. The nasal bone is broad 

 in the Salmon, but varies in shape in other fishes. In the genus Lophius and in the Diodonts it is 

 unossified, being represented by membrane. The nasal bone completely divides the nasal cavity into 

 two lateral pits. Between the orbits there is often a partition, which is sometimes cartilaginous and 

 sometimes membranous. The turbinal bones of man, on which the olfactory nerve is spread out, are 

 represented in the fish, and placed at the sides of the nasal bones. The nasal bone sometimes supports 

 teeth, and teeth are frequently found on the palatine bones. 



The sense capsules are well fitted into cavities of the skull in bony fishes. The auditory 

 organ becomes blended with the cartilaginous base of the skull in Lepidosiren, and there are distinct 

 otic bones, which protect the labyrinth of the ear in many bony fishes. These auditory capsules 

 are often closed externally, but have a wide opening into the cranial cavity. The eye in cartilaginous 

 fishes is contained in a cartilaginous capsule, but in most osseous fishes the capsule is bony. Bony 

 plates are developed in some fishes in the sclerotic or hard outermost covering of the eye. In 

 most fishes the bony orbits for the eyes communicate with each other, but the Shads, Hydrocyon, 

 Syiibranchus, Cyprinus, and many other genera have a bony septum between the orbits, and in the 

 Ganoid fishes of the genera Lepidosteus and Polypterus the orbits are divided, as among the Batrachia, 

 by a double septum, which forms the walls of the olfactory prolongation of the brain. 



The bones which form the jaws may conveniently be considered together. They are somewhat 

 differently arranged in fishes to their condition in other animals, but the bones are still easily identified 

 by the same names ; thus pterygoid, palatine, maxillary, and pre-maxillary still mark the order of 

 succession of the bones of the palate from behind forward. The palatine bones unite in front with 

 the maxillary, pre-frontal bone, and vomer, though in some fishes certain of the attachments are made 

 by ligaments. The palatine usually forms the roof of the mouth as well as the floor of the orbit, and 

 is always short and broad in the fishes with broad heads and small mouths, and long and slender in 

 the fishes with wide mouths. The presence or absence of teeth on the palatine bone furnishes an 

 excellent character for distinguishing many genera. The maxillary bone is usually small and 

 toothless, and lies between the palatine bone behind and the pre-maxillary in front. In shape it is 

 usually like the pre-maxillaiy, but more slender. In the Salmon tribe it unites with the hinder end 

 of the pre-maxillary, which is short, and carries teeth along its mai-gin. This condition also occurs in 

 the Herring family, while in the Plectognathi, or Globe-fishes, the maxillary and pre-maxillary are 

 blended into one bone. In the genus Lepidosteus these bones, although forming a single toothed border to 

 the upper jaw, are subdivided into several bony pieces, but in the genus Polypterus the maxillary shows 

 no signs of subdivision. This bone is very small in the Siluroid fishes, and both it and the pre-maxillary 

 are entirely wanting in some of the Eels. The pre-maxillary bones are usually movably connected 

 together at their anterior ends, but in the genus Diodon they are completely blended. The blended 

 pre-maxillaries form the sword-like weapon in front of the snout carried by the Sword-fish (Xiphias) 

 and by the Gar-pike. The pterygoid and transverse bones are not always present, though they occur 

 in the majority of fishes. In the Salmon tribe and Eels they are blended with the palatine, and in 

 some other fishes, like the genera Lophius and Synodon, they are entirely absent. Both these bones some- 

 times support teeth. The mandible, or lower jaw, is sometimes united in the median line in front by 

 bony union, but sometimes the union is made by ligament. In front there is a bone which carries the 

 teeth, called the dentary bone. This usually contains within it a cartilage, which is known as 

 Meckel's cartilage, and the other bones placed behind the dentary are arranged around this 

 cartilage. The lower jaw, however, joins the skull in osseous fishes in a way that is quite unparalleled 

 among other animals. There is a distinct arch formed by a series of bones, which supports both the 

 mandible and the gill-covei', and this arch is prolonged up the sides of the head, so as to unite with 

 its side in the auditory region. The mandibular arch, however, is not altogether distinct from 

 another arch placed behind it, which is termed the hyoid arch, and corresponds with the bones which 

 in higher animals are connected with the tongue. The several portions of the hyoid have received 



