SKELETON OF SKATE 595 



From the ear capsule to the articulation of upper and 

 lower jaw there extends on each side a club-shaped cartilage, 

 which connects the jaws with the skull, known as the hyo- 

 mandibular or suspensorium. It is the upper half of the 

 second arch. Attached to it is a slender four-jointed rod — 

 the lower half of the hyoid arch. 



Then follow five branchial arches, each primarily four- 

 jointed, forming the framework of the gill-bearing region. 



Of less importance are the labial cartilages about each 

 nasal capsule, an antorbital cartilage uniting the nasal 

 capsule with the end of the pectoral fin, and a spiracular 

 or meta-pterygoid cartilage supporting the rudimentary gill 

 in the spiracle. 



The pectoral girdle forms an almost complete hoop of 

 cartilage attached dorsally to the crest of the vertebral plate. 

 The ventral region is distinguished as the coracoid, and is 

 separated from the dorsal or scapular region by three facets, 

 to which the three basal pieces of the pectoral fin are fixed. 

 A separated portion of the girdle forms the supra-scapula, 

 which connects the scapula with the crest of the vertebral 

 plate. 



Of the three basal pieces of the fin, the anterior or 

 propterygium and the posterior or metapterygium are 

 large, the median or mesopterygium is small. AH bear 

 jointed radials, which are parts of the endoskeleton ; a 

 few radials articulate directly with the shoulder-girdle (see 

 Fig. 335). The true fin-rays, comparable to the dermal 

 rays in the fins of Bony Fishes, are represented by " horny " 

 (or, more strictly, elastoidin) fibres. These are inter- 

 cellular products of mesoderm (mesenchyme) cells. 



The pelvic girdle is simpler than the pectoral, and is not 



pterygo-quadrate cartilage [p.q.) or Ripper jaw ; Meckel's 

 cartilage (.1/.) forming the lower jaw ; and the hyo-mandibular 

 (h.m.) which suspends the jaws to the skull. A little farther 

 back are seen the five branchial arches and the anterior hyoid 

 arch ; h.br., the fifth hypobranchial ; v.pl., the vertebral plate. 

 At the right is seen the skeleton of the paired fins, at the left 

 the surface of the skin with the sensory tubes {s.t.) ; sc, the 

 scapular region of the shoulder-girdle, with the scapular 

 fontanelle ; c, the coracoid region ; p.pt., the anterior basal 

 cartilage or pro-pterygium ; ni.pt., the meso-pterygium ; 

 mt.pt., the ineta-pterygium — all three bear jointed radials, 

 while a few, as shown here, articulate directly with the 

 shoulder-girdle ; pti., pubic bar of pelvic girdle ; St., stomach ; 

 S.V., spiral valve of intestine. 



