THE ELASMOBRANCHIl. 



113 



of an Elasmobratich consisting, exclusively, of cartilaginous 

 representatives of the primary palato-quadrate arch and of 

 Meckel's cartilage. 



The former of these, the so-called upper jaw, may either 

 be represented, as in the Ghimmra (Fig. 33), by the anterior 

 portion {S, D) of a triangular cartilaginous lamella, which 

 stretches out from the sides of the base of the skull, and is 

 continuous with the representative of the hyomandibular sus- 

 pensoriura ; or there may be, on each side, a cartilaginous bar 

 movably articulated in front with the fore-part of the skull ; 

 and, posteriorly, furnishing a condyle, with which the ramus 

 of the lower jaw, representing Meckel's cartilage, articulates. 



In the latter case, which is that met with in the Sharks 

 and Rays (Figs. 34 and 35), a single cartilaginous rod (g) is 

 movably articulated with the skull, in the region of the peri- 

 otic capsule, upon each side ; and, by its opposite extremity, 

 is connected by ligamentous fibres both with the palato- 

 quadrate (A) and with the mandibular or Meckelian cartilage 

 {^Mn). This cartilaginous suspensorium represents the liyo« 



Fig. 83. — Vertical section of the skull of CMm,os/ra nwnstrosr.^ without the labial and nasdl 

 cartilage s: j4, the basi-occipital regrion; P, the pituitary fossa ; JVa, partition between 

 the olmctory sacs ; JS, alveolus for the anterior upper-jaw tooth ; 0, D, the rejrion of the 

 trianf^lar cartilage which answers to the hyomandibular and quadrate ; D, B, that 

 which answers to the quadrate, pterygoid, and palatina ; Jfft, the mandible ; / Or, the 

 interorbital septum ; asc and psc^ the anterior and posterior semicircular canals ; I., II., 

 v., VIII., exits of the olfcetory, optic, fifth and eighth pairs of nerves. 



mandibular and the symplectic bones of the Teleostei, and 

 gives attachment to the hyoidean apparatus (-Hy). The lat- 



