Fish are bony scales, gill breathing, swimming through the tail and trunk and the coordination of fins swimming and feeding by the upper and lower jaws, belonging to the chordate phylum of vertebrates, generally people divide vertebrates into fish (53%), birds (18%), reptiles (12%), mammals (9%), amphibians (8%). According to the statistics of the late Canadian scholar "Nelson" in 1994, there are 24618 species of living species fish in the world, accounting for more than half of the named vertebrates, and new species of fish are constantly being discovered, with an average of about 150 species per year, which should have increased by more than 1500 species in more than a decade, and the current global named fish species are about 32100 species.
<h3>overview</h3>
Zhu Xuanxian Chinese painting "Hibiscus Goldfish"
The bones of fish are divided into two categories according to their nature: cartilage and hard bone. Cartilaginous fish retain cartilage throughout life, and there is a calcareous precipitate in the cartilage, also known as calcified cartilage. The bones of the bonefish are mainly hard bones, which are divided into two kinds of softened hard bone and periosteum according to different forms: the hard bone formed by ossification on the original basis of cartilage is softened hard bone, such as vertebrae, ear bone, occipital bone, etc.; the hard bone formed by direct ossification of dermis and connective tissue is called membrane bone, such as frontal bone, parietal bone, gill cap, etc. The bones of fish are divided into two parts, the central axis bone and the appendage bone, according to the part.
<h3>Appendage bones</h3>
Appendage bones are divided into odd fin bones and even fin bones. The dorsal, and caudal fin bones in the odd fin are supported by the fin bones (spoke bones) inserted into the muscle, and the fin bones of the teleost fish are also called fin bones. The even-fin skeleton consists of two parts: the band bone (shoulder strap and lumbar bone) and the fin bone (the fin bone and the fin strip). In fish, except for the shoulder strap of the teleost fish, all the appendage bones are not directly related to the spine, which is also one of the characteristics of fish, which is determined by the way the fish moves by swimming.
fish
<h3>Divided into skull and spine</h3>
(1) The largest number of skulls: The skull of a teleost fish is composed of about 130 pieces of bone (referring to existing fish, and the skulls of primitive fish in ancient times can be as many as 180 pieces), which is the animal with the largest number of brain bones in vertebrates. The skull of a fish is divided into two parts: the cranial skull and the pharyngeal skull.
The painter Li Zhenkai has been more than a year old
(1) The skull of the cartilaginous fish is a cartilage cavity to protect the brain, the structure is simple, there is no demarcation and suture, only the back of the brain is covered by a membrane, such a skull is called a soft skull. There are several pieces of occipital bone, ear bone, sphenoid bone, and sieve bone ossified from the soft skull of cartilaginous fish, as well as the nasal bone, frontal bone, parietal bone, plough bone and other membranous cranial parts derived from the membrane bone, so the structure is very complex. The skull of a teleost fish is synthesized from many pieces of bone to form the main part of the skull.
(2) Vertebrates start from fish, pharyngeal arch differentiation into upper and lower jaws, wells form pharyngeal cranium, fish pharyngeal cranium is the most developed, formed by 7 pairs of ">" shaped pharyngeal arch, the first pair is enlarged into a jaw arch, the dorsal section of the jaw arch is called palatal cartilage, and the abdominal segment is called Michael's cartilage. The two constitute the upper and lower jaws of cartilaginous fish. The appearance of the upper and lower jaws is more advanced than that of the round mouth, and it can actively consume food. The durodete fish evolved into the membranous premaxilla and maxilla, replacing the cartilage maxilla (palatine cartilage), Mychonnes cartilage evolved into the joint bone, tooth bone and corner bone of the cartilage, etc. The second pair of tongue arches is composed of both sides of the tongue and jaw cartilage, tongue cartilage and central, basal tongue cartilage, mainly for the support of the tongue, but also to help support the upper and lower jaws, the 3rd to 7th pairs for the gill arch, supporting the gill and gill septum, so that the gills are separated from each other, which is conducive to breathing.
(2) Spine replaces the spine: The spine of fish is composed of many vertebrae connected to each other to form a columnar bone to replace part or all of the backsteord, which has the function of supporting the body and protecting the spinal cord and major blood vessels, which is more advanced than that of round mouths. The vertebrae of fish have the characteristics of inward depression on both sides of the front and back, called two concave vertebral bodies or double concave vertebral bodies, which are unique to fish, and the remaining spinal cord can be seen in the adjacent two vertebral space and the small tubes that run through the vertebral body. Vertebrates start with fish, and the basic structure of the vertebrae has been formed. The vertebrae of both cartilaginous and teleost fish are divided into vertebral bodies, myelin arches, myelin spines, chalcedonial arches, and pulsal spines. Among them, the vertebral body is the main part, the ribs are connected to the transverse process of the vertebrae, and the ribs of the teleost fish are mostly more developed.
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