OCR Text |
Show 60 MR. NELSON ANNAN BALE ON [Feb. 7, parasphenoid, extending along nearly tlie whole length of the cranium. The auditory capsules had fused with the cranium and were well-developed, although there was no external tympanic membrane visible. The orbital arches were not formed, but the structures connected with the gills had entirely disappeared. The dorsal surface of the cranium is divided longitudinally by a simple suture, which expands behind into a wedge-shaped cleft. The first seven vertebrae are normal in structure and, with the exception of the neural spine, thoroughly ossified; those of the tail are imperfectly ossified and retain their identity. The eighth and ninth vertebrae are abnormal; they are fused together, the anchylosis being complete on the dorsal surface but incomplete on the sides and below. The dorsal surface is nearly flat, but a slight ridge can be detected running along the mid-dorsal line, and there is a small mound-like elevation towards the left side on the eighth vertebra. The transverse and articular processes are deformed and asymmetrical in a manner and to a degree best shown in PI. Y L figs. 1 6, l / t lg. On the right side the only trace of the pelvic arch that can be distinguished is a minute, irregularly-shaped fragment of bone imbedded in a. broad ligament which is attached at one end to the right transverse process of the ninth vertebra and ends in the muscles of the body-wall at the other. On the left side, in the corresponding position, there is a sac lined with connective tissue in the body-wall; it does not communicate either with the exterior or with the body-cavity. Its shape is an elongated oval, sloping from near the dorsal 'surface forwards and downwards towards the belly in front of the vent. A hernia, not strangulated but containing a portion of the intestine, projects into it in front. Lying in this sac, but terminating above and below in the body-wall, is a sickle-shaped bone, which appears to have been provided with muscles not continuous with those of the body-wall. Unfortunately they are much decomposed. The bone is only fixed to the walls of the sac by adhesions of connective tissue. Above it is attached to the left transverse process of the ninth vertebra by a ligament resembling that on the right side. It slopes downwards, forwards and inwards, terminating in an expansion lodged in the muscles of the belly just in front of the vent, which has a mesial position. Its curve is slight, as is shown in fig. 1 j, which represents it as seen from in front when held vertically; fig. 1 h gives a view of the inner surface when the bone is lying in a horizontal position. The relationship between it and the eighth and ninth vertebne is accurately represented in fig. 1 f , but the ligament has been omitted. Considering the form and relationships of this bone, there can be no doubt that it represents the left ilium, though its position and forward slope are abnormal. The ligament which attaches it to the vertebra must represent not only its own head but also the distal extremity of the transverse process. The fragment of bone and the ligament on the other side of the body similarly represent |