Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/56

52 portion, which extends across behind the precoracoid foramina; a strong elevated rib extends across the posterior face at this point. The outer margin of the coracoid is thickened, rounded and slightly concave.

The form of the posterior margin of the coracoidea is unknown, and they are much broken on the inner margin. They may have been considerably longer than in the accompanying cut.

The greater part of the pelvic arch appears to be preserved. From the obliquity of the median suture and from the form of the pubes as they are preserved on a large nodule of indurated clay, it is evident that they have formed a boat-shaped support to the abdominal viscera, with an obtuse keel on the median line below. ` The following diagram will explain the relation of its parts.

The anterior and lateral portions of the pubes are very thin, as are also the median posterior portions of the ischiadic plates. The pubic bones are thickest on the posterior margin; they present a downward projecting median convexity near the anterior end. Depth of the articular face, 2 in., 8 lin.

The superior surface of this arch was brought to light by the exertions of my friends, B. Waterhouse Hawkins and Wm. M. Gabb, who removed a large mass of matrix which fortunately accompanied and protected it. This presents a transverse thickening extending across it, and continuous with the posterior margin of the clavicles. A median longitudinal thickening extends from this to the anterior margination, embracing in its angle with the transverse, a shallow concavity. The posterior projection which is continuous with the median part of the ischia, is strongly deflexed behind the transverse rib, and is continuous with the basin-like concavity formed by the united pubes. The glenoid surface of the pubes is a sigmoid, while that of the ischia is regularly convex. The articulation of the ilium has been exclusively with the former.

Of the pleurapophysial portion of the two arches nothing appears to be preserved except two lateral symmetrical long bones. One was found imbedded in the mass carrying the pelvic arch, and they articulate well with the pubes; but the articular extremity is too short to articulate with ischia at the same time. Though they resemble the inferior view of the procoracoids, they represent the ilia of Plesiosaurus. The head is subdiscoid, rather flat, slightly projecting excentrically with a ligamentous pit. The articular surface is very oblique to the axis of the shaft, and is separated from the surface by a marked angle all around. Nothing like a trochanteric ridge is apparent in this bone.