XIII 



PHYLUM CHORDATA 



177 



Callorhynchus, lies just externally to the mandible, nearly equalling 

 it in size and having the appearance of a secondary or external 

 jaw. In Callorhynchus the snout is supported by three cartilagi- 

 nous rods growing forward from the cranium, of which one (r) 

 is median and dorsal and represents the rostrum ; these, as well as 

 the great lower labial (Fig. 801, Ib 3 .), are represented by com- 

 paratively small structures in Chimsera. 



The hyoid resembles the branchial arches in form and is little 

 superior to them in size. Above the epihyal (Fig. 801, e. Ay.) is a 

 small cartilage (ph. hy.), evidently serially homologous with the 

 pharyngo-branchials, and therefore to be considered as a pharyngo- 

 hya.L It represents the hyo-mandibular of Elasmobranchs, but, 



v.o.s 



p.s.c 



FIG. 801. Chimsera monstrosa, lateral view of skull, a. s. c. position of anterior semi- 

 circular canal ; c. hy. cerato-hyal ; e. hy. epi-hyal ; fr. cl. frontal clasper ; h. s. c. position of 

 horizontal semicircular canal ; i. o. s. inter-orbital septum ; Ib. 1, Ib. 2, Ib. 3, labial cartilages ; 

 Mel: c. mandible ; Nv. 2, optic foramen ; Nv. 10, vagus foramen ; olf. cp. olfactory capsule ; 

 op. r. opercular rays; pal. qu. palato-quadrate; ph. hy. pharyngo-hyal ; p. s. c. position of 

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



having no function to perform in the support of the jaws, it is no 

 larger than the corresponding segments in the succeeding arches. 

 Long cartilaginous rays (op. r.) for the support of the operculum 

 are attached to the cerato-hyal. 



The first dorsal fin is remarkable for having all its pterygio- 

 phores fused into a single plate, which articulates with the 

 coalesced neural arches already referred to. The remaining fins 

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



VOL. II N 



