174 



ZOOLOGY 



SECT. 



lates with the dorsal portion of the first branchial arch. In the 

 Sharks the hyoid is usually relatively massive ; in the Rays it is 

 smaller, and in most cases closely resembles the branchial arches, 

 and bears similar cartilaginous rays ; a larger or smaller median 

 element, or basihyal, is present in all cases. 



There are always five pairs of branchial arches except in 

 Hexanchus and Chlamydoselachus, which have six, and Heptanchus, 



Pio. 835.— Skeleton of Sting-Ray (Urolophus testac.eus), ventral view. a. v. p. anterioi- 

 vertebral plate ; bos. br. baiibranchlal plate ; 6i-.l— (ii-.s branchial arches. (The branchial rays 

 are not represented , the round dots indicating their articulations with the arches. ) ci. skeleton 

 of clasper ; h. m. hyomandibular ; htj. hyoid arch ; tub. labial cartilage ; liri. ligament connect- 

 ing the hyomandibular with the palatoquadrato and Meckel's cartilage ; Mck. Meckel's carti- 

 lage ; ms. pt. mcsopterygium, and iiU. pt. metapterygium of pectoral fln ; mt. pt'. metapterygium 

 of pelvic fin ; nas. nasal cartilage ; pat. palatoquadrate ; p«f. pectoral arch ; pt. pelvic arch ; 

 2:iro. pt. proptcrygium ; sjj. spiracular cartilage. 



in which there are seven. Their dorsal ends are free in the 

 Sharks, articulated with the anterior vertebral plate of the spinal 

 column in most Rays. Tllxternally they bear a series of slender 

 cartilaginous hrancMal rays. The median ventral elements of the 

 branchial arches are usually more or less reduced, and in some 



