The sacrum is a large triangular bone at the bottom of the spine.
In addition to this broad membrane, there is a rounded fasciculus, superficial to the rest, which reaches from the base of the styloid process of the ulna to the lunate and triangular bones.
The medial articulates with the triangular bone by an oblong facet, cut obliquely from above, downward and medialward.
The scientists recovered the left half of the pelvis, 18 vertebrae and a structure called the sacrum, a thick, triangular bone at the lower end of the spinal column.
The medial surface is marked by a smooth, quadrilateral facet, for articulation with the triangular bone.
The fifth runs between the adjacent margins of the triangular and pisiform bones.
As for the septomaxilla mentioned in the title of the reference: "A small, triangular bone is placed between the premaxilla and the maxilla; this bone is interpreted as a septomaxilla.
The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone.
In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage.
The hip bone first appears in fishes, where it consists of a simple, usually triangular bone, to which the pelvic fin articulates.