t present known [November, 



TN many birds, as the ^tomorphse, Psittacomorphse, Coraco- 

 -^ morphae of Huxley, we find at the back and upper part of the 

 glenoid cavity, a sesamoid long known to ornithotomists as the 

 os humero-scapulare ; this bone can in no way be claimed as be- 

 longing to the category of bones that enter the pectoral limb, as 

 it increases the articular surface of the glenoid cavity, and in so 

 doing properly belongs to the scapular apparatus, being accessory 

 to the shoulder girdle. 



In the arm Jwe have then but one bone, the humerus, in the 

 forearm, or antibrachium, we find two, the radius and ulna, and 

 in the angle formed by the articulation of the latter two with the 

 humerus, or the elbow, we detect in many birds (Turdidae and 

 others), lodged at its posterior aspect, quite a sizable sesamoid, 

 crescentic in form, which seems to serve the purpose of protect- 

 ing the joint. It reminds one not a little of a floating olecranon. 

 Two of these sesamoids occur at the same locality among Guille- 

 mots and Penguins (Owen). 



Among raptorial birds and in some few other families, we find 

 articulating with one or both of the long bones of the antibrach- 

 ium, at the distal end or ends as the case may be, another sesa- 

 moid, the os prominens. 



The vast majority of adult birds, and indeed the writer does 

 not recall a'single exception at this moment, possess two free 

 carpal bones, the scapho-lunar and cuneiform. To these we have 

 to add to our enumeration, several bones that are found in the 

 wrist of some, but not all immature birds; these eventually, we 

 know, all become anchylosed about the proximal extremities of 

 the metacarpals. First in this list we have os magnum, the larg- 

 est, that subsequently amalgamates with index metacarpal ; next 

 in order we discover the unciform (Morse), a diminutive segment 

 found in some birds, that finally unites with the last metacarpal, 

 and to these four the writer, two or three years ago, added a fifth 

 and called it the pisiform. For several reasons, however, I have 

 been induced to change the name of this segment, and have done 

 so in a memoir elsewhere, now in press, and called it the pentos- 

 teon, it being the fifth carpal segment discovered up to date. The 

 name is one that cannot be productive" of harm nor confusion 



