124 



the well-turned prominent ball terminates the back part of the centrum rather more obliquely, 

 its aspect being backwards and upwards. The hypapophysis is developed in different pro- 

 portions from different vertebrae, but throughout the greater part of the tmnk presents a 

 moderate size. A vascular canal perforates the under surface of the centrum, and there are 

 sometimes two or even three smaller foramina. A large, vertically oblong, but short dia- 

 pophysis extends from the fore part of the side of the centrum obliquely backwards : it is 

 covered by the articular surface for the rib, convex lengthwise, and convex vertically at its 

 upper half, but slightly concave at its lower half. The base of the neural arch swells out- 

 ward from its confluence with the centrum, and developes from each angle a transversely 

 elongated zygapophysis ; that from the anterior angle looking upwards, that from the 

 posterior angle downwards, both surfaces being flat, and almost horizontal, as in the Batra- 

 chians. A thick rounded ridge connects the anterior with the posterior zygapophysis on 

 each side, extending along the base of the neural arch. The neural canal is narrow, with a 

 subtrihedral area, and with a narrow longitudinal ridge on each side. The neural spine is of 

 moderate height, which scarcely equals its antero-posterior extent ; it is compressed and trun- 

 cate. A wedge-shaped process (the ' zygosphene' *) is developed from the fore part of the 

 base of the spine ; the lower apex of the wedge being, as it were, cut off, and its sloping 

 sides presenting two smooth, flat, articular surfaces. This wedge is received into a cavity 

 (the 'zygantrum't) excavated in the posterior expansion of the neural arch, and having two 

 smooth articular surfaces to which the zygosphenal surfaces are adapted. 



Thus the vertebrae of Serpents articulate with each other by eight joints in addition to 

 those of the cup and ball on the centrum ; and interlock by parts reciprocally receiving and 

 entering one another, like the joints called tenon-and-mortice in carpentry. 



The neural spine is broad, moderately high, compressed and truncate superiorly. The 

 hypapophysis of the anterior vertebrae is narrower and more pointed ; in the middle and 

 posterior abdominal vertebrae this process is represented by a low tubercle, which in the 

 posterior abdominal vertebrae terminates in a ridge. In the caudal vertebrae the hypapo- 

 physis is double, the transition being effected by a bifurcation of the tubercle in the posterior 

 abdominal vertebrae. The diapophyses become much longer in the caudal vertebrae, and 

 support in the anterior ones short ribs which usually become anchylosed to their extremities. 

 In the present series of vertebrae, two of the caudal vertebrae present the anomaly of being 

 anchylosed with each other, with the interposition of an additional left half of the neural 

 arch, a left diapophysis, and left division of the neural spine : the left half of the neural arch 

 belongs to the second vertebra, whilst the left supernumerary diapophysis and hypapophysis 

 are developed from the first or anterior vertebra. 



Presented by Dr. Wallich, F.R.8. 



604. The atlas or first trunk -vertebra of a large African constricting Serpent (Python 



The hypapophysial part of the centrum seems to form the entire body of the vertebra ; it 

 is wedge-shaped, as usual in Reptilia, and is articulated by suture on each side to part of the 



* Zvyot, a yoke, a^y, a wedge. t Zvyot, and avrpor, a cavity. 



