186 



ZOOLOGY 



SECT. 



The hyoid resembles the branchial arches in form and is little 

 superior to them in size. Above the epihyal (Fig. 860, e. hy.) 

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

 pharyngobranchials, and therefore to be considered as a pharyngo- 

 hyal. It represents the hyomandibular of Elasmobranchs, but, 

 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 ceratohyal. 



The first dorsal fin is remarkable for having all its pterygiophores 

 fused into a single plate, which articulates with the coalesced 



neural arches al- 

 ready referred to. 

 The remaining 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 

 fenestrse closed by 

 membrane, one of 

 them of great size 

 in Callorhynchus. 

 The skeleton of the anterior clasper articulates with the pubic 

 region. 



Digestive Organs. The teeth (Fig. 861) are very characteristic, 

 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 palatine teeth (pal. t.), and in the lower jaw a single pair 

 of large mandibular teeth (mnd. t.). They 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 whiter colour than the rest of the tooth, and known 

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



FIG. 860. Chimerra monstrosa, lateral view of skull. 

 a. s. c. position of anterior semicircular canal ; c. hy. 

 ceratohyal ; e. hy. epihyal ; fr. cl. frontal clasper ; h. s. c. 

 position of horizontal semicircular canal ; i. o. s. interorbital 

 septum ; Ib. 1, Ib. 2, Ib. 3, labial cartilages ; Mck. C. mandible ; 

 Nv. 2, optic foramen ; Nv. 10, vagus foramen; olf. cp. olfactory 

 capsule ; op. r. opercular rays ; pal. qu. palatoquadrate ; 

 ph. hy. pharyngohyal ; p. s. c. position of posterior semi- 

 circular canal ; qu. quadrate region ; r. rostrum. (After 

 Hubrecht.) 



