1??67.J 269 [Wyman. 



the fibula of the Monotremes. No evidence is brought forward to 

 prove that the sesamoid referrcid to is in any way different from the 

 bones found in tendons in other parts of the body, as e.g., in the heads 

 of the gastrocnemius of the opossums, and also of many rodents, and in 

 the flexor tendons of the fingers and toes of many mammals, in the 

 peroneus longus in man, and as an anomaly in the tendon of the 

 human biceps cruris near its insertion into the fibula. Furthermore, 

 the part in question can hardly be considered as a detached epiphysis, 

 since in those animals where a sesamoid is developed in the tendon 

 over the head of the fibula, the normal epiphysis exists in the bone 

 itself. 



In the Penguin it does not appear that the part corresponding to 

 the olecranon is of any less size than in other birds, although the sesa- 

 moid bones, which Prof. Owen supposes replace this process, are pres- 

 ent. In the arm of a lai'ge Pteropus we have found the patella-like 

 bone attached to the ulna by a ligament, as the patella is attached to 

 the tibia. The ulna, however, has a pi'ojection at its upper end of 

 about the same size as the olecranon in birds. But before tliis patella- 

 like bone can be claimed to be a detached epiphysis, it must be ascer- 

 tained whether the ulna has, or has not, an epiphysis in the immature 

 bone. In many of the anatomical descriptions of the ulna, the ole- 

 cranon process and the epiphysis have been described as if they were 

 the same thing, which most certainly they are not. In mammals the 

 olecranon Is often much longer than in man, the epiphysis forming but a 

 very small part of it. and in man Is only a very thin scale covering its 

 end. Properly speaking, the olecx-anon is a continuation of the shaft 

 of the ulna. The cartilage of ossification Interposed between the shaft 

 and the epiphysis is remarkably thick, and has given rise to the belief 

 that this was itself the epiphysis. The last only forms at a late period. 



As to the argument drawn from the great development of the pro- 

 cess on the top of the fibula in the Ornithorhynch us, It seems to us 

 that this is an instance in which we are liable to be misled by form, 

 and that the resemblance between the process in question and the 

 olecranon is no proof of homology. It should be remembered that 

 processes, and even bones, in different animals, are liable to every de- 

 gree of variation according to the physiological requirements In indi- 

 vidual cases. Compare the extraordinary processes of the humerus 

 of the Mole, the jNIylodon, or of the Ant-eatei's, with the diminutive 

 ones of the same bone in the Three-toed Sloth, the Cetaceans, or of 

 the marine Saurian reptiles. Tiie olecranon Itself is a very variable 

 process; it does not exist in Cetaceans, is hardly apparent in birds and 

 most reptiles, but In mammals may become, as in the great Armadillo, 

 almost half as long as the whole ulna. This development is in relation 

 to the extensor muscles of the fore arm. The remai'kable develop- 



