In the Lamprey[192] (Fig. 124) the paired parachordals and trabeculae together form a trough-like chondrocranium, which has only a fibrous roof, except where a slender _synotic_ band of cartilage extends between the two periotic capsules. The floor is also incomplete, a large pituitary fontanelle remaining to indicate the original separation of the trabeculae while transmitting the hypophysial or pituitary caecum. The notochord traverses the floor of the parachordal portion of the cranium as far as the pituitary fontanelle, and from the sides of the synotic ring the auditory capsules project in the shape of conspicuous lateral prominences. In front the otherwise open end of the cranial cavity is closed by the dorsally-placed and unpaired olfactory capsule, which is perforated behind by two apertures for the olfactory nerves, and has only a fibrous connexion with the cranial walls. Anteriorly to the olfactory capsule the cranial floor is prolonged forwards over the roof of the mouth as a large laterally-expanded plate, formed by the united anterior portions of the trabeculae, and no doubt representing the _mesethmoid_ cartilage of the Dog-Fish. So far the cranium presents no special difficulty, and in its general features may be readily compared with that of an embryonic Elasmobranch. As for the rest of the skull, it is obvious that it has been greatly modified, partly to form and to support the skeletal framework of the remarkable suctorial buccal funnel, and partly to form the singular rasping lingual apparatus. Hence it is always difficult and sometimes impossible to identify with {218}certainty the component parts as being represented in other Craniates. On each side of the cranium, beneath the eye, there is a characteristic V-shaped _subocular arch_. Of its two legs the hinder one is continuous above with the periotic region of the cranium, and the other with the anterior trabecular region, while the pointed apex is directed obliquely downward and forward. From the hinder margin of the posterior limb a slender _styloid process_ passes downward in the side wall of the pharynx, and terminates below in a forwardly directed _cornual_ cartilage. A velum, fringed along its free margin with a series of tentacles, projects forwards into the oral cavity from between the oral apertures of the oesophagus and the branchial canal, and probably serves to prevent the entrance of foreign particles to the gill-sacs. This valve-like velum is supported by a _velar skeleton_, consisting of two lateral cartilages which are prolonged into the tentacles, and extend transversely between the inner surfaces of the two styloid processes. The apex of each subocular arch is connected with a small and somewhat triangular cartilage (_postero-lateral cartilage_), which is directed upward and forward, and lies in the side wall of the oral cavity. With some degree of probability the subocular arch may be compared to the palato-quadrate cartilage of a