The =dorsal= and =anal= fins each consist of two sets of structures, the =fin-rays= and the =interspinous bones=. Each fin-ray forms a delicate, nearly straight, bony rod which becomes thickened and bifurcated at its proximal or vertebral end, while distally it is transversely jointed and flexible, frequently also becoming more or less flattened. The first dorsal fin has thirteen rays, the second, sixteen to nineteen, the third, seventeen to nineteen. The first anal fin has about twenty-two, the second anal fourteen. In each fin the posterior rays rapidly decrease in size when followed back. The =interspinous bones= of the dorsal and anal fins alternate with the neural and haemal spines respectively, and form short, forwardly-projecting bones, each attached proximally to the base of the corresponding fin-ray. The =caudal fin= consists of a series of about forty-three rays which radiate from the posterior end of the vertebral column, being connected with the urostyle or hypural bone, and with the posterior neural and haemal spines without the intervention of interspinous bones. Like the other fin-rays those forming the caudal fin are transversely jointed, and are widened and frayed out distally. The tail-fin in the Cod is =homocercal=, i.e. it appears to be symmetrically developed round the posterior end of the vertebral column, though in reality a much greater proportion is attached below the end of the vertebral column than above it. It is a masked heterocercal tail. THE SKULL. Owing to the fact that very little cartilage remains in the skull of the adult Codfish, its relation to the completely cartilaginous skull of the Dogfish is not easily seen. Before describing it therefore, the skull of the Salmon will be described, as it forms an intermediate type. THE SKULL OF THE SALMON[36]. The Salmon's skull consists of (1) the =chondrocranium=, which remains partly cartilaginous and is partly converted into cartilage bone, especially in the occipital region, (2) a large series of plate-like membrane bones. THE CHONDROCRANIUM. This is an elongated structure, wide behind owing to the fusion of the large auditory capsules with the cranium, and elongated and tapering considerably in front; in the middle it is much contracted by the large orbital cavities. DORSAL SURFACE OF THE CRANIUM. In the centre of the posterior end of the dorsal surface is the =supra-occipital= (fig. 9, A, 1) with a prominent posterior ridge. It is separated by two tracts of unossified cartilage from the large series of bones connected with the =auditory organ=. The first of these is the =epi-otic= (fig. 9, 2), which is separated by only a narrow tract of cartilage from the supra-occipital, and is continuous laterally with the large =pterotic= (fig. 9, A, 3) which overlaps in front a smaller bone, the =sphenotic= (fig. 9, 4). Both epi-otic and pterotic are drawn out into rather prominent backwardly-projecting processes.