10 



. The jaws and branchial arches, note — 



(a) The upper jaw (palato-pterygoid arch). 



(b) The lower jaw (mandibular arch). 



(c) The hyomandibular cartilage connecting the jaws to the lower portion of 



the auditory capsule. 



(d) The small spiracular cartilage (metapterygoid) between the hyomandibular 



cartilage and the auditory capsule. 



(e) The hyoid arch articulating with the hyomandibular, and composed of a 



dorsal epihyal, a median ceratohyal, and a ventral small hypohyal 

 segment. 



(/) The five branchial arches composed of (from above downwards) pharyngo-, 

 epi-, cerato- and hypo- braiichial portions, — note that the hypobranchial 

 portions of the first brancMal arch meet in the middle line, to form a 

 narrow bar slightly behind the lower jaw ; that the hypobranchials of the 

 fifth arch meet in the middle line to form a large basibranchial plate 

 with a pair of anterior horns ; and that the pharyngobranchials of the 

 fourth and fifth arches unite with each other. 



Note the pair of elongated thymus glands lying dorsal to the pharyngo- 

 branchials. 



Make a sketch showing the jaws and branchial arches from below. 

 . The pectoral girdle and pectoral fins, note — 



(a) That the two sides unite in the middle line forming a bar — the coracoid 

 portion of the girdle — across the body on the ventral surface. 



(6) The two halves on the dorsal surface, forming the scapular portions of the 

 girdle. 



(c) The small supra-scapular portions, forming the attachment of the girdle to 



the vertebral plate. 



(d) The three glenoid facets on each external edge of the girdle, which form 



articulating surfaces for the fins. 



(e) The three fontaneUes on each side. 

 (/) The three divisions of each fin, viz. — 



(1) The long propterygium, articulating with the anterior glenoid facet, 



and composed of several pieces, one of which reaches the antorbital 

 cartilage. 



(2) The small mesopterygiimi articulating with the middle glenoid facet, 



(3) The long metapterygium, which consists of several pieces, and 



articulates with the posterior glenoid facet. 

 (g) The long jointed cartilaginous fin rays. 

 Sketch the pectoral girdle and one of the fins. 



