160 



ZOOLOGY 



.SECT. 



already been described. The main differences observable in the 

 different families are connected with the size and form of the 

 rostrum. In the Rays the lower lip of the foramen magnum is 

 deeply excavated for the reception "of a^short process, the so-called 

 odontoid process, which projects forwards from the anterior vertebral 



lab 



has. b 



FIG. 788. Skeleton of Sting- Ray (Urolophus testac'eus), ventral view. . r. p. anterior 

 vertebral. plate ; bas. br. basi-branchial plate ; br. 1 br. -5 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. hyomaiidibular ; liy. hyoid arch ; lal>. labial cartilage ; 

 lig. ligament connecting the hyomandibular with the palato-quadrate and Meckel's cartilage ; 

 Mck. Meckel's cartilage ; ms. pt. mesopterygium ; mt. pt. metapterygium of pectoral fin ; 

 mt. pt'. metapterygium of pelvic fin ; nas. nasal cartilage ; pal. palato-quadrate ; pect. pectoral 

 arch ; pi. pelvic arch ; pro. pt. propterygium ; sp. spiracular cartilage. 



plate, and on either side of this is an articular surface the occi- 

 pital condyle for articulation with corresponding surfaces on that 

 plate. In the Sharks the skull is fused with the spinal column. 

 The apertures of the aqueductus vestibuli in the Rays- are not 

 situated in a median depression such as is observable in the Dog- 

 fish and in all the Sharks. The articular surface in the auditory 



