1. rostrum. 2. olfactory capsule. 3. ethmo-palatine process. 4. palatine portion of palato-pterygo-quadrate bar. 5. quadrate portion of bar. 6. Meckel's cartilage. 7. teeth. 8. labial cartilage. 9. hyomandibular. 10. postorbital process. II. optic foramen.] Two pairs of labial cartilages (fig. 16, B, 8) are often present. They lie imbedded in the cheeks outside the anterior region of the jaws, and are specially large in _Squatina_. As regards the visceral arches[44] the simplest and most primitive condition of the jaws is that of the Notidanidae, in which the mandibular and hyoid arches are entirely separate. In these primitive fishes the palato-pterygo-quadrate bar articulates with the postorbital process (fig. 16, 10), while further forwards it is united to the cranium by the ethmo-palatine ligament. The hyoid arch is small and is broadly overlapped by the mandibular arch. The term =autostylic= is used to describe this condition of the suspensorium. From this condition we pass in the one direction to that of _Cestracion_ (fig. 16, B), in which the whole of the palato-pterygo quadrate bar has become bound to the cranium, and in the other to that of _Scyllium_. In _Scyllium_ (fig. 6), while the ethmo-palatine ligament is retained, the postorbital articulation of the palato pterygo-quadrate has been given up, so that the palato-pterygo quadrate comes to abut on the hyomandibular and is attached to it by ligaments. The pre-spiracular ligament (fig. 16, 20) running from the auditory capsule also assists in supporting the jaws. Lastly we come to the purely =hyostylic= condition met with in Rays, in which the mandibular arch is entirely supported by the hyomandibular. In some Rays the hyoid is attached to the posterior face of the hyomandibular near its proximal end, and may even come to articulate with the cranium. The =visceral arches of Elasmobranchs= may be summarised as follows:-- 1. The =mandibular arch=, consisting of a much reduced dorsal portion, the pre-spiracular ligament, and a greatly developed ventral portion from which both upper and lower jaws are derived. The mandible (Meckel's cartilage) is the original lower member of the mandibular arch, and from it arises an outgrowth which forms the upper jaw or palato-pterygo-quadrate bar. In _Scymnus_ this bears a few branchiostegal rays. 2. The =hyoid arch=, which consists of the hyomandibular and the hyoid, and bears branchiostegal rays on its posterior face. [Illustration FIG. 17. DORSAL VIEW OF THE BRANCHIAL ARCHES OF _Heptanchus_. (From GEGENBAUR). 1. basi-hyal. 2. cerato-hyal. 3. second hypo-branchial. 4. first cerato-branchial. 5. first epi-branchial. 6. first pharyngo-branchial. 7. pharyngo-branchial, common to the sixth and seventh arches. 8. basibranchial of second arch. 9. basibranchial, common to the sixth and seventh arches.]