In considering the first class, he commences with articular cartilage, which he describes at great length in the various stages of its de- velopement, and at the different periods of Hfe. He gives in detail the account of numerous dissections of the ovum and foetus illustrating the first stage, during which he shows that no blood-vessels enter into the substance of any of the textures composing a joint ; but that the changes its component parts undergo, are effected by the nutrient fluid from the large blood-vessels, by which, at this stage, each articulation is surrounded. In the second stage of the develope- ment of articular cartilage, the author shows, by numerous dissec- tions, the process by which the blood-vessels are extended into the substance of the epiphysal cartilage, and converge towards the at- tached surface of articular cartilage, and how, at the same time, blood-vessels are equally prolonged over a certain portion of its free surface. He shows that none of these blood-vessels enter the sub- stance of the articular cartilage, and he points out that in them the arteries become continuous with the veins ; first, by their terminating in a single vessel, from which the veins arise ; secondly, by their forming large dilatations from which the veins originate ; and, lastly, they become directly continuous with the veins in the formation of loops of various characters. In the third stage, that which is exhi- bited in adult life, the epiphysal cartilage is converted into osseous canceUi. These contain large blood-vessels, which are separated from the articular cartilage by a layer of bone composed of corpus- cles, and the author beheves that the principal source of nutrition to this tissue is the nutrient fluid which exudes into it from these vessels, by passing through the articular lamella just noticed. The free surface of adult articular cartilage is nourished by vessels which pass to a shght extent over it. The author points out the presence of fine tubes which pervade the attached portion of adult articular cartilage, to which he ascribes the function of transmitting through its substance the nutritive fluid derived from the vessels of the can- celli. He also advances the opinion that the articular cartilage be- comes thinner during the whole of life, by being gradually converted into bone.
Fibre -cartilage constitutes the second tissue of the first class. The author first enters upon an examination of its structure ; and in order to arrive at some definite conclusions on this subject, whereon anatomists of all ages have so much differed, he made numerous dissections of fibro-cartilages in the different classes of animals at various periods of their developement, the results of which he details. He arrives at the conclusion that this tissue is composed of carti- laginous corpuscles and of fibres ; the latter preponderating in adult life, the former in infancy ; and that during life the corpuscles are gi-adually converted into fibres. He enters at length into the ques- tion of the vascularity of these cartilages ; and from a careful study of many injected specimens of man and animals at various periods of their developement, the particular results of which he relates, he believes that blood-vessels are contained only in their fibrous portion, and have the function of nourishing that which is cartila-
