The skull (Fig. 75) is modified in a very peculiar manner. The brain-case is short, broad, and high, in fact almost spherical. The supraoccipital bone rises upwards and forwards from the foramen magnum, to meet the frontals at the vertex, thus completely excluding the parietals from the upper region of the cranium. The frontals are expanded laterally to form the roof of the orbits. The anterior narial aperture opens upwards, and has in front of it a more or less horizontally prolonged rostrum, formed of the maxillæ, premaxillæ, vomer, and mesethmoid cartilage, extending forwards to form the upper jaw or roof of the mouth. There are no clavicles. The humerus is freely movable on the scapula at the shoulder-joint, but beyond this the articulations of the limb are imperfect, the flattened ends of the bones coming in contact with each other, with fibrous tissue interposed, allowing of scarcely any motion. The radius and ulna are distinct, about equally developed, and much flattened, as are also all the bones of the manus. There are four, or more commonly five digits, and the number of the phalanges of the second and third digits always exceeds the normal number in mammals, sometimes very considerably (hyperphalangism); they present the exceptional character of having epiphyses at both ends.[123] The pelvis is represented by a pair of small styliform bones placed longitudinally, suspended below and at some distance from the vertebral column at the commencement of the caudal region. These appear to represent the ischia, as the crura of the corpora cavernosa are attached to them. In some species, to the outer surface of these are fixed other small bones or cartilages, the rudiments of the hind limb. [Illustration: FIG. 75.—A section of the skull of a young Dolphin (_Globicephalus melas_) × ⅕. _PMx_, Premaxilla; _Mx_, maxilla; _ME_, ossified portion of the mesethmoid; _an_, anterior nares; _Na_, nasal; _IP_, interparietal; _Fr_, frontal; _Pa_, parietal; _SO_, supraoccipital; _ExO_, exoccipital; _BO_, basioccipital; _Sq_, squamosal; _Per_, periotic; _AS_, alisphenoid; _PS_, presphenoid; _Pt_, pterygoid; _pn_, posterior nares; _Pl_, palatine; _Vo_, vomer; _s_, symphysis of mandible; _id_, inferior dental canal; _cp_, coronoid process of mandible; _cd_, condyle; a, angle; sh, stylohyal; _bh_, basihyal; _th_, thyrohyal. (From Flower’s _Osteology of Mammalia_.)]