FIG. 12. DEFORMED JOINT BETWEEN TWO CAUDAL VERTEBRAE OF A DINOSAUR (Apatosaurus) caused by the growth of a tumor-mass, which on account of its extreme vascularity represents possibly an haemangioma, or some similar pathological growth.

FIG. 13. MICROSCOPIC SECTION OF A PORTION OF THE PERIPHERY OF ABOVE TUMOR, showing arrangement of lacunae, vascular spaces (a) and lamellae of bone. How much this differs in arrangement of elements from normal bone remains to be determined.

has described these sufficiently in other places to make their characters well known. The most interesting lesion seen among the dinosaurs has been regarded as resembling a modern hemangioma (Figs. 12-13). Fig. 14 will show the nature of the

5" Pathologic Lesions among Extinct Animals: A Study of the Evidences of Disease Millions of Years Ago," Surgical Clinics of Chicago, Vol. 2, No. 2, pp. 319-331, Figs. 108-116, 1918.

vascular spaces and the arrangement of the osseous trabeculae as seen in a sagittal section of the tumor mass.

FIG. 14.

PHOTOGRAPH, ENLARGED, OF THE CUT SURFACE OF THE TUMOR SHOWN IN FIG. 12, to show the arrangement of the trabeculae of bone and the large vascular spaces (areas outlined in ink). The large area at the top of the figure is apparently a portion of the intravertebral space, which has become largely obliterated by the growth of the tumor. The substance of the chevron, seen in Fig. 12 as portion of the tumor, has been incorporated, when seen in section, with the mass of pathological bone.

CRETACEOUS

The diseases of the mosasaurs may be taken as a sample of the prevalence of disease and injury among the vertebrates of the Cretaceous. These aquatic vertebrates, as well as their congeners, the plesiosaurs and dinosaurs, were afflicted with a variety of diseases and the writer has been able to study the details of the lesions on the fossils from the Cretaceous of Kansas. Twenty years age Doctor Williston called attention to the diseased nature of the arm bones of one of the Cretaceous mosasaurs. Recently I have been able to study these bones (Fig. 15). Their pathological nature and the exostoses of a hyperplastic nature are at once evident (Fig. 15). A tentative diagnosis of osteoperiostitis has been given as the cause of the lesions. Microscopic study of the lesions (Figs. 16 and 17) reveals the bony lamellae laid down in a concentric manner, as if to form Haversian systems. The lacunae are relatively large

VOL. VII.--18.

FIG. 15. HUMERUS OF A MOSASAUR, Platecarpus coryphaeus, from the Niobrara of Kansas showing the details of pathological lesions resembling those seen in modern osteoperiostitis. The microscopic sections (Figs. 16-17) were taken from the lesion at A. The disturbance also involved the articular surfaces indicating the presence of an arthritic infection.

and are provided with short canaliculi, and there are areas where osteoid tissue (Fig. 16) is present, comparable in every way with osteoid tissue, seen in modern cases of osteomyelitis. For the first time in the history of paleohistology perforating fibers of Sharpey (Fig. 17) are seen running through the sections.

A dorsal vertebra of Platecarpus, a well-known mosasaur from the Cretaceous of Kansas, presents an extremely interesting example of an osteoma (Fig. 18), the only one thus far known in a fossil condition. The specimen has not yet been studied microscopically, but a gross examination of a sawn section (Fig. 19) through the osteoma and vertebra shows in a very interesting manner how the tumor mass grew out of the vertebra. An X-ray examination of the bone reveals nothing of importance.

A radius of another mosasaur shows on the proximal surface an extensive necrosis. Sections of the bone show hyper

FIG. 16. PHOTOMICROGRAPH OF THE PORTION OF THE LESION (A, Fig. 15), showing osteoid tissue. The black lacunae are seen to be without canaliculi and their arrangement in concentric lamellae suggests the presence of an Haversian system. The dark area running obliquely out of the lower left hand corner is a post fossilization fracture filled with calcite. This area of osteoid tissue in the humerus of a mosasaur, 15,000,000 years old, is identical in anatomical structure with osteoid tissue from the human humerus in a case of osteomyelitis.

trophy of the peripheral substance. The nature of the organism producing the necrosis is not determined, but the fossil presents an exact duplicate of modern instances of extensive arthritic necrotic sinuses, which result in hypertrophy and the production of numerous osteophytes.

Dollo has described dental caries in a mosasaur jaw, with a hyperplasia of the bone with accompanying necrosis, as if the creature had suffered from a mouth infection similar to modern alveolar pyorrhea. The results are identical in modern and ancient bones.

The prevalence of disease reached a climax in the mosasaurs, dinosaurs, plesiosaurs and turtles of the Cretaceous, and with the opening of the Tertiary the incidence of disease went sharply down, to rise again with the rise of mammalian life and reach a very high point during the Pleistocene.

FIG. 17. MICROSCOPIC STUDY OF ANOTHER AREA OF THE SAME SECTION AS THAT SHOWN IN FIG. 16, showing the presence of perforating fibers of Sharpey, the long black fibers running obliquely through the figure, and small lacunae with short canaliculi, without any definite arrangement into systems.

FIG. 18. A DORSAL VERTEBRA OF A MOSASAUR, Platecarpus, from the Niobrara of Kansas, showing on the posterior (right hand of figure) end of the vertebra an osteoma, the only known fossil representative of this type of tumor.

EOCENE

The extinction of the large groups of reptiles at the close of the Cretaceous doubtless brought about the disappearance also of many forms of disease which attacked these animals. Some forms of disease, as seen in the lesions left on the fossil