192 



ZOOLOGY 



SECT. 



coalesced neural arches already referred to. The remainiag fins 

 are formed quite on the Elasmobranch type, as is also the shoulder 

 girdle. The right and left halves of the pelvic arch are separate 

 from one another, being united in the middle ventral line by 

 ligament only; each presents a narrow iliac region and a broad 

 flat pubo-ischial region perforated by two apertures or fenestra 

 closed by membrane, one of them of great size in Callorhynchus. 



4- 





/J.S.C 



V 



i^. lO 



Fig. .S4'.i.— Chimsera monstrosa, lateral view'uf skull. n. x. <;. position of iiiitorior seiiii- 

 circular canal; c. hy. ceratoliyal ; e. hy. epihyal ; fr. cl. fronted clasper ; h. s. c position of 

 lioriisoiital semicircular canal ; i. o. x. interorliital septum ; lb. 1, 10. i. 10. J, labial cartilages ; 

 Mck. c. mandible ; Nv. :.', optic foramen ; iVr. 10, vagus foramen ; olf. cy). olfactory capsidc ; 

 op. r. opercular rays ; jrial. qu. palatoquadrate ; ph. hy. pharyngohyal ; p. .s. <■. position of 

 posterior semicircular canal ; qu. quadrate region ; )•. rostrum. (After Hubrecht.) 



The skeleton of the anterior clasper articulates with the pubic 



region. 



Digestive Organs. — The teeth (Fig. 850) are very cliaracter- 

 istic, having the form of strong plates with an irregular surface 

 and a sharp, cutting edge. In the upper jaw there is a pair of 

 small 'Vomerine teeth (vo. t.) in front, immediately behind them 

 a pair of large ^a/a^me teeth (pal. t.), and in the lower jaw a single 

 pair of large mandilndar teeth (mnd. t.). Tliey are composed of vaso- 

 dentine, and each palatine and mandibular tooth has its surface 

 slightly raised into a rounded elevation of a specially hard sub- 

 stance, of wliiter colour than the rest of the tooth, and known 

 as a iritor (tr.). The stomach is almost obsolete, the enteric canal 

 pa?sing in a straight line from gullet to anus ; there is a well- 

 developed spiral Ttoltc in the intestine. 



Respiratory Organs. — There are three pairs of holohranchs or 

 comnlete uills borne on the first three branchial arches, and two 

 hemibranchs or half-gills, one on the posterior face of the hyoid, 



