BETWEEN TYPICAL llEPTILES AND OTHEK ANIMALS. 179 



bones than are usual with mammals. The claw-phalanges are pro- 

 portionally longer than in Orycteropus ; but in that animal they 

 are compressed from side to side, and not from above downward. 



§ 2. The Avian Gharacters of Chelonians. 



There is no resemblance between the Avian and Chelonian 

 crania, except in the immaterial point that both are toothless, 

 ■and both, in an immature condition, liave members which show 

 transitional indications of teeth. In the lower jaw both have the 

 denta,ry bone similarly single [typically]. And the number of 

 elements in the lower jaw is seemingly often the same, though, 

 from the obliteration of sutures in birds, the number of bones is 

 not always easily determined in the mature animal. 



In the marine Chelonia the length of the neck-vertebrss is like 

 that in the Penguin. In Testudo there is an approximation, both 

 in length and in form, to the anterior vertebrae of long-necked 

 birds, such as the Heron or Swan ; but the bird never has the 

 centrum so free from lateral processes as Testudo, never has 

 the zygapophyses prolonged so far forward, and never departs in 

 the neck from the Avian articulation. The dorsal region of Che- 

 lonians is so much modified in relation to the immovable carapace 

 that detailed comj)arison is impossible. It may be noticed that 

 the underside of the dorsal centrum is often smooth and rounded 

 as in such birds as the Heron. 



The sacrum has nothing in common. The tail is similar in such 

 birds as the Swan and in Testudo, correspondence being seen in 

 the short centrum flat on the underside, the depressed neural arch 

 devoid of neural spine, in the transverse process coming off from 

 the base of the centrum. In place of the chevron bones seen 

 in some freshwater Chelonians, birds rarely have more than a 

 mere ossicle between the vertebrae, approximating to the interver- 

 tebral ossicle of Lizards, or a few vertebrae have long double hy- 

 papophyses after the manner of Serpents. 



The form of the Chelonian pectoral arch, consisting of scapula 

 and coracoid, is closely paralleled by Struthious birds. The elon- 

 gated coracoid in the young bird is about intermediate in length 

 between that of the marine and land types ; but in Chelonians 

 the bones have no distal articular surface, not meeting any ster- 

 num. The scapula in Chelonians is straighter and more cylin- 

 drical ; it gives oif near the articulation with tlie coracoid a digital 

 process which Mr. Parker names the precoracoid, and which in 



LINN. JOUEN. — ZOOLOGY, VOL. XII. 13 



