170 THE ANATOMY OF VERTEBKATED ANIMALS. 



A great palato-pteiygoid osseous arcli (D) extends from 

 the middle line along the upper and the under surface of 

 the palato-quadrate arch on each side to near the articular 

 surface of the mandible. In the middle of the roof of the 

 mouth, divergent, cutting, dentary plates are developed upon 

 it. An osseous nodule lies in the articular head of the palato- 

 quadrate cartilage, and is continuous with the bone F. 



The mandible presents dentary plates corresponding with 

 those of the palate, and biting between the latter. The 

 hyoidean arch is attached to the posterior and lower edge 

 of the suspensorium — which bears a bony ray representing 

 an operculum — while the hyoidean arch itself carries a 

 single bi-anchiostegal ray (Br, Fig. 52). 



The pectoral arch is composed of a median cartilaginoixs 

 liart, with two lateral portions of cartilage, at once separated 

 from, and connected with, the median cartilage by bone. 

 The bone is separated from the cartilage by a layer of 

 connective tissue, and seems to represent the clavicle, while 

 the cartilage answers to the coalescent coraco-scapular 

 cartilages of other fishes. 



The filiform fin is supported by a many-jointed carti- 

 laginous rod, articulated proximally with the coraco-scapular. 

 Upon this are disposed fine fin-rays like those of the Elas- 

 mobranchs, which support the marginal fringe of the fin. 

 The ventral fin has the same structure as the pectoral. 



The intestine possesses a spiral valve, and the rectum 

 opens into a cloaca. The lungs have remarkably stiff walls, 

 and extend through the greater part of the body, beneath 

 the spine. The glottis, opening upon the ventral wall of 

 the gullet, places them in communication with the cavity 

 of the mouth, into which the nasal sacs open by posterior 

 apertures, which lie inside the upper lip and constitute true 

 posterior nares. The heart has a small, but distinct, left 

 auricle, into which the blood which has been aerated in the 

 lungs is returned. In addition to lungs, Lepidodren pos- 

 sesses both internal and external giUs, but the latter are 

 rudimentary in the adult. 



The different species seem to differ in the manner in which 



