390 



MANUAL OF ZOOLOGY 



SECT. 



may be nearly completely cartilaginous (Hexanchus and 

 Hcptanchus}, but usually the centra are strengthened by 



tab 



tas. 



FIG. 233. Skeleton of sting-ray (UrolOpllUS testaceus), ventral view. a. v. /, 

 anterior vertebral plate; bas. br, basi-branchial plate; br.i-br.j, branchial 

 arches. The branchial rays are represented as having been removed, the round 

 dots indicate their articulations with the arches cl, skeleton of clasper; h, m, 

 hyomandibular; ky, hyoid arch; lab, labial cartilage; lig, ligament connecting 

 the hyomandibular with the palato-quadrate and Meckel's cartilage; mck, 

 Meckel's cartilage; ms. J>t, mesopterygium; mt.pt, metapterygium of pectoral 

 fin; ml.pt', metapterygium of pelvic fin; nas, nasal cartilage; pal, palato- 

 quadrate ; pect, pectoral arch ; //, pelvic arch ; pro. pt, propterygium ; sp, spiracu- 

 lar cartilage. 



