The true transverse processes are represented by tubercles situated on the superior borders of the articular processes of each of the vertebræ of the lumbar region. Apropos of these different osseous processes, we are reminded that they are also present in the human skeleton. In the horse the costiform processes of the fifth and sixth lumbar vertebræ articulate, and are sometimes ankylosed, one with the other; the terminal ones articulate with the base of the sacrum. Sometimes the processes of the fourth and fifth are thus related; this is the case in the figure (4) given; here the costiform processes of the fourth and fifth vertebræ articulate, and the two terminal ones have coalesced. In the ox, the same processes are more developed than in the horse; their summits elevating the skin, produce, especially in animals which have not much flesh, prominences which limit the flanks in the superior aspect. The costiform processes of the last lumbar vertebræ are separate from each other; those of the latter are not in contact with the sacrum. =The Sacrum.=[3]--This bone, single and median, is formed by the mutual coalescence of several vertebræ, which vary in number according to the species observed. [3] In human anatomy, the sacrum and the coccyx are studied as part of the pelvis; we, therefore, in the study of the artistic anatomy of man, study these bones with the bones of the lower limbs. Here we do not follow this plan. In animals the sacrum and the coccyx, as a matter of fact, clearly continue the superior border of the skeleton of the trunk; hence we study them with the vertebral column. _Vertebræ Constituting the Sacrum._--Bears, 5; dogs, 3; cats, 3; rabbits, 4; swine, 4; horses, 5; camels, 4; oxen, 5; sheep, 4. The sacrum is situated between the two iliac bones; with which it articulates, and contributes to the formation of the pelvis. It is obliquely placed, from before backwards, and from below upwards; immediately behind the lumbar section of the vertebral column; and is continued by the coccygeal vertebræ, which form the skeleton of the tail. It is triangular in outline, and is generally more narrow in proportion than in the human being. All things considered, it is more large and massive, and of greater density, in species which sometimes assume the upright posture, rather than in those which cannot assume that attitude; for example, the sacrum of the ape, of the bear, of the dog, and of the opossum are proportionately larger than those of the horse.[4] [4] This is particularly striking only in those portions of the sacrum that are not in relation with the other bones of the pelvis. We think that the general form of this bone depends on the mode of its connexions with the iliac bones and the extent of the articular surfaces by which it is in contact with the latter.