114 



gin. On the inner side, between the trenchant plate and the splenial piece, there is a narrow 

 longitudinal patch of denticles. 



The body of the atlas extends forwards like a short odontoid process above the interspace 

 between the occipital condyles. A short parapophysial and diapophysial plate is developed 

 from each side of the atlas, which has posterior hut not anterior zygapophyses. In the 

 second vertebra, which has increased in length, the par- and di-apophysial plates have united 

 to form a compound transverse process, which supports a short straight pleurapophysis ; and 

 a strong hypapophysial ridge is developed from the whole length of the under surface of the 

 centrum. A ridge is continued from the diapophysial ridge to the posterior zygapophysis. 

 Two vertical ridges diverging to the same processes from the fore part of the neural arch 

 represent the neural spine. In the third vertebra the characters are assumed, which have 

 been noted in the description of No. 576. 



Hunterian. 



577. Five caudal vertebrae of the Siren lacertina. 



Each vertebra is compressed, and its vertical extent increased, by the bending down of the 

 parapophysial plates, to form two vertical walls, intercepting a hoemal canal which protects 

 the vascular trunks of the tail. The diapophysial ridge is continued outwards from the side of 

 the centrum. The neural arch has coalesced with the centrum in this, as in other Batrachia. 



Hunterian. 



578. A vertically and longitudinally bisected vertebra, from the middle of the back 



of the Siren lacertina. It shows the depth and shape of the terminal articu- 

 lar excavations of the centrum, which were filled, as in fishes, by unossificd 

 remains of the notochord, in the condition of concentric ligamentous layers, 

 with intervening gelatinous fluid, the whole inclosed in a capsule, and giving 

 a certain elasticity to the vertebral column *. Hunterian. 



579. The horny dental sheaths of the jaws, with the palatal villiform teeth of the 



Siren lacertina. Hunterian. 



Genus Proteus. 



580. A considerable portion of the vertebral column, with the mandible and hyoid 



apparatus of the Proteus anguinus. 



In the entire skeleton the third to the ninth vertebra; support minute ribs attached to the 

 lower (parapophysial) half of the transverse process : they are wanting in the twenty-one 

 following vertebrae, and re-appear well developed in the thirty-first vertebra, where they form, 

 with broad cartilaginous hsemapophyses, a pelvic arch. 



* Sec the Wet Preparation, No. 246. Physiological Series, Gallery. 



