I20 ZOOTOMY. 



the right side; place the fish in the supine 

 position (dorsal surface downwards) and fasten 

 out the mandible, hyoid, and gill arches right and 

 left, so as to get a good view of the interior of the 

 mouth. Observe the following : — 



159. The numerous small premaxillary teeth arranged 

 in two symmetrical sets on the premaxillse. 



160. The larger mandibular teeth on the lower jaw. 



161. The median crescentic group of vomerine teeth, 

 a short distance behind the premaxillary teeth. 



162. The superior pharyngeal teeth, arranged in 

 four groups, two on each side, on the ankylosed pharyngo- 

 branchials (§ 57). 



163. The inferior pharyngeal teeth, one group on 

 each of the small fifth branchial arches (§ 62). 



164. The small, blunt, non-protrusible tongue, supported 

 by the median ventral portion of the hyoid arch. 



165. The absence of posterior nares or spiracles. 



166. The branchial clefts, vertical fissures between 

 the gill arches, five in number, the first being between the 

 hyoid and first branchial arches, the last between the fourth 

 and fifth branchials. 



167. The gill-rakers, horny filaments acting as strainers, 

 attached to the branchial arches, and bounding the margins 

 of the clefts. 



168. The greatly constricted aperture of the oesophagus. 



169. The pseudobranchia has been already noticed 

 (§ 90) : on removing the mucous membrane, it is seen to 

 be a rounded vascular body, resembling the rete mirabile 

 in the air-bladder. 



XXXI. Remove a portion of one of the gills on the 

 left side, and make out by dissection and trans- 

 verse sections 



