Vol. 6g.~] SKELETON OE OBNJTHODESMUS LATIDENS, 383 



however, is not seen on the left side ; but this may be due 

 to pressure. The neural arches overhang; the centra, forming a 

 ledge along the median region of their sides. The surfaces of 

 these arches are alternately concave and convex in anteroposterior 

 extent. The convexities occur where the zygapophyses have fused, 

 and underneath these a series of fossae are found (PI. XXXVIII, 

 fig. 5, F., F.). Of these fossas that of the first vertebra is the largest,, 

 the others decreasing in size to the last vertebra. Probably pneu- 

 matic foramina occur within the inter-vertebral fossa?, as they are 

 not present elsewhere. On the dorsal surfaces of the. transverse 

 processes, the matrix is too hard, and they themselves are too 

 fragile, to permit of its removal, and this is so likewise between the 

 hinder three ; but their ventral surfaces have been fully exposed. 

 These processes arise partly from the neural arches, and partly from 

 the centra. In the first notarial vertebra, as in the last cervical, 

 they originate on the anterior half of the centra, and gradually 

 extend more and more on each following vertebra, until in the fifth 

 and sixth their bases occupy the length of the centrum. They are 

 entirely free, one from the other, and are directed slightly upwards. 

 They are arranged in three pairs, and each pair is different in size 

 and form. The first pair are expauded at their bases and outer 

 extremities, and contracted medially. The middle pair are weaker 

 and shorter than the others, and their distal borders are produced 

 posteriorly into a style-like process. The ultimate pair are con- 

 siderably broader than the rest, are quadrate in shape, and are as 

 long as the first pair. Their ventral surfaces are concave, with 

 a curious downward turning of the anterior edge. This is also 

 seen in the transverse process of the fourth vertebra. The spaces 

 between the transverse processes are greatest, between those of the 

 first and second vertebras ; between the others they decrease, until 

 between the last two the division has become narrow. The centra 

 are comparatively small; their ventral surfaces are convex from 

 side to side, and feebly concave longitudinally. The first three 

 show a lateral concavity, the last are free from any. grooving. 

 On the hinder, lateral, ventral borders of the centra of the first 

 three vertebras, at their point of union, occur protuberances ; these. 

 I take to be parapophyses. 



The Dorsal Vertebrae. 



The dorsal vertebras are six in number and amphiplatyan.. 

 They decrease very rapidly in dimensions backwards. The neural 

 spines are thinner, not so high, and the neural arch less expanded 

 than in the notarial vertebras. The transverse processes, instead of 

 occupying a horizontal position, as in the vertebras of the notarium, 

 at once begin to assume an upright one, until in the fourth they 

 are nearly vertical. The centra are convex from side to side ; but, 

 through the raising of their anterior and posterior edges, they are- 

 longitudiually more or less concave. 



