1072 



KCAXDIXAVIAN KISIIKS. 



cartilage, which is (lircctcd tVoiii tlic tip nt' the rostral 

 cartilage (B) to the roof of tlie nasal capsule on the 

 same side. These t\\'o lateral cartilages and the rostral 

 cartilage thus huild up a tju'ee-sided pyraniidifbrni case, 

 within which is enclosed the fibrous capsule wherein 

 the ampulla' hereafter to be described have their ca;cal 

 base. In the HoloccpliaJi — wliere, as in the generality 

 of deep-sea fishes, the rostral system of the lateral line 

 is particularly well developed — tlie soft snout and the 

 said capsule are supported by a pair (fig. 294, J)\) of 

 cartilaginous rods, widely se})arated at the bases but 

 converging towards the ti))s, with tlie bases resting on 

 the snout in front of the nasal capsules, and by an 



The morphological Iximologues of tlie jawliones of 

 the Teleosts and the higher vertel)rates also appear in 

 the Klasmobranchs under the guise of labial cartilages. 

 The Klasmobranchs are in general ra])toi-ial fishes of a 

 pronounced type, with powerful teeth in the mouth; hut 

 these teeth are set, not on the jawbones proper, hut 

 on the predecessors, in the development (jf the verteb- 

 rate type, of the palate and lower jaw. on the palato- 

 quadrate cartilage (fiifs. 21)4 and 21IS, <ji)ij) and the 

 so-called Meckelian cartilage (J/A') of each side, the 

 predecessors of the lower jaw, which cartilages appear 

 even in the embryos of the highest vertebrates as gra- 

 dually evanescent rndimcnts in the structure of the 



ptoh 



),t oh I j) 



y^^ 



ptp 





fo>wf- 

 im,h- 



/ 

 ' '1', 



'I' 



Ints Imv 



rai/ foDi Off 

 B 



Fig. 299. Skull of a Tope {Galeorhimis), seen from the left (A) and from above (B). After Gegenbaur. 

 ro, nuiiinent of occipital crest; fonpf, prefrontal fontanelle; ie, incisura ethmoidalis. Tin- otlier letters are explained in tlic prei 



unpaired, thicker and firmer cartilaginous rod {h\), set 

 on the bridge of the snout lietween the two anterior 

 oi)eniMgs of the ethmoidal canal (rt'), a confluence of 

 the anterior parts of the preorbital ((7;) and orbitonasal 

 {on) canals. The males also pos.sess a similar carti- 

 laginous rod (//) above the preorbital process, free and 

 mobile, transformed to a ])rehensile organ set with 

 teeth, and probably serving to hold the female during 

 copulation. The history of evolution has not yet elu- 

 cidated the morphological significance of these carti- 

 laginous rods in the Nnloci-jilidli, but from this point 

 of view they should probably be ranged, one and all, 

 beside the labial cartilages of the Sliai'ks. 



mandible. The relation of the ])alato(|ua(lrate cartilage 

 to the skull we have already considered. At the jws- 

 terior (tiuadrate) extremity it articulates with the 

 ]\lecke!ia,ii cartilage, which here functionates as a lower 

 jaw, so that the two pairs of cartilages form a ring 

 around the gape. But these cartilages, especially the 

 ;\Ieckelian, are closely united behind by ligaments to 

 the hyoid arch, an opening (the spirai'le, fig. 298, spir) 

 being left, however, between the quadrate i'Ji^g) and 

 the hyomandibular {hm) cartilages, and the anterior 

 margin of this spiracular canal being furnished either 

 with a more or less developed cartilaginous disk (.?i)c), 

 answering to the meta|)terygoid lione of the Teleosts, 



