The patella exists in all placental Maninzals, but is absent in many Marsupials. In Birds it is usually, but not invariably, present ; there are even sometimes two, one placed above another. In those aquatic birds which have the tuberosity of the tibia prolonged upwards as a large process, a patella is always found placed just behind it*, sometimes closely adapted to it, and extending beyond it so as apparently to form its summit.-I-. No patella has been met with in any reptile.
Other sesasnoid bones.— Opposite the plan tar aspect of the distal joint of the fore and hind foot of Solipedes, there is a long super numerary bone, called by farriers the shuttle bone, placed transversely. This, like the sesamoid bones above described, enters into the composition of the subjacent joint ; a broad slip of the perforans tendon is inserted into its proximal side, whilst on the distal side a portion of the synoyial capsule alone, and that not so strong as one would expect, attaches it to the ungual phalanx ; the main part of the tendon passes over it to be inserted into the ungual phalanx, leaving a cavity lined by a synovial membrane between itself and the sesamoid bone in question. This bone re minds one of that which, as above mentioned, is occasionally found at the distal joint of the thumb and great toe in the human subject.
Small bones are found in one or both heads of the gastroenemins in all Manimalia except Man, the Seals, Pig, and all Ruminants but Cervus, in which genus they are found, yet only in the external head of the muscle.
A sesamoid bone is met with in the inser tion of the tendo Achillis of certain Birds, as the capercailzie ; and the tendons of the legs of birds are very commonly ossified, not, how ever, where they correspond to the joints.
Use. — Sesamoid bones serve much the same purpose as processes for the muscles that are inserted into them, without the incon venience inseparable from a process, of giving an angular form to the joint. They also pro tect the long flexor tendons at points where perhaps they might be injured. But after all, taking into consideration all the facts related above, and many others that have presented themselves to me in the course of this inquiry, I cannot but believe, that some higher law than that of adaptation concurs in deter mining the presence, if not the size, of even these little bones.
(S. R. Pittard.)