1. A series of experiments on adult rabbits was carried out in which a tendon was transplanted and embedded in a bony tunnel and traversed a joint after the manner of a tenodesis.

2. Histological observations were made on the reaction of surrounding bone and tendon at intervals over a period of 307 days.

3. The findings suggest that the buried tendon undergoes a process of progressive degeneration, and that host cells issuing from the adjacent bone marrow infiltrate and ultimately replace it by new tendon tissue.

4. The invading cells are believed to be derived, as a result of the provocative stimuli provided by the experiment, from primitive reticular cells of the haemopoietic tissue.

5. The tunnelled bone undergoes considerable remodelling and associated with this is the presence of a considerable number of osteoblasts and osteoclasts.

1. The normal anatomy of the intervertebral disc of immature rabbits is described.

2. An account is given of the changes that occur after an operative incision in the ventral part of the intervertebral discs of rabbits which allowed the escape of the nucleus pulposus. The account is based on observations made on fifty-five young animals killed at intervals during the twenty-five months after operation.

3. The superficial part of the wound in the annulus heals rapidly by active fibrosis. Thereafter there is a chondrification of the ventral region of the disc, followed by ossification. A prominent bony ridge ultimately ankyloses the vertebrae adjoining the disc.

4. The site of the nucleus pulposus is eventually occupied by a dense pad of fibrocartilage. A tongue of this tissue projects into the deep median part of the wound which remains unhealed.

5. A hypothesis is submitted regarding the mechanism of rupture of the annulus fibrosus and prolapse of the nucleus pulposus in man; this hypothesis is based in part on the observations of lesions in discs not subjected to operation.