THE TOUCANS AND BARBETS. 325 



intimate relationship of these two groups. And I may take this oppor- 

 tunity to point out some further peculiarities which these birds have in 

 common with each other. These are : 



(1) The great extent of the deltoid muscle, which extends down the 



entire length, or very nearly so, of the humerus, and is inserted by a P- z - S. 1882, 

 tendinous slip into a small tubercle on the external surface of that bone, 

 close to the elbow, and just above the tubercle for the tendon of origin 

 of the extensor metacarpi radialis longior muscle. This is common to 

 the Picidae, Indicator, and the Toucans and Barbets. As long ago noticed 

 by Nitzsch *, this peculiarly long deltoid also occurs in the Passeres ; but 

 its similar condition in the Capitonidae has not, I think, before been 

 observed. But, as showing that the similarity in this respect of the 

 Passeres to the Picidae and their allies is not necessarily a mark of 

 relationship, I may add that in some other birds, as, e. g., Carpophaga, 

 Ptilopus, and Cariama, the deltoid is nearly the same in size and shape, 

 extending down to very near the elbow. 



(2) The presence of a distinct ossicle, of the nature of a sesamoid, the 

 so-called " scapula accessorial which is developed in the scapulo-humeral 

 ligament of the shoulder-joint, and plays over the posterior angle of the 

 humerus-head. From it arise some of the fibres of the deltoid. 



Nitzsch, with his usual accuracy t, had also noticed the existence in the 

 Picidae of this bone, which, as is well known, occurs also in the Passeres ; 

 but the relationships of the bone in the last are not the same as they are 

 in the Picidae, Indicator and other Pici I have examined. 



In the Passeres the bone in question becomes connected with the 

 tendon of the pectoralis secundus muscle as this courses over the head of 

 the humerus towards its insertion, sending round it a special thin 

 tendinous loop, in which the tendon of that muscle plays. Hence, in 

 the undisturbed position of these parts, the pectoralis tendon is seen to 

 be somewhat L- shaped, the angle of the L being at the place where it is 

 connected by this fibrous loop to the sesamoid bone, and so dragged 

 backwards out of a direct course. 



In the Pici I have been able to find no such connection between the 

 scapula accessoria and the pectoralis secundus tendon, which remains 

 quite free from it throughout its course. 



The additional points of resemblance detailed in the present communi- 

 cation render the near relationship of the Picidae to the Capitonidae even 

 more certain than before. Nitzsch, from pterylographical grounds, and 

 Kessler J, from osteological ones, long ago pointed out this connection, 



* Zeitschr. f. ges. Naturwiss. 1862, xix. p. 400. 

 t Tom. supra cit. p. 399. 

 { Bull. Soc. Imp. Nat. Moscou, xvii. pp. 332-334, 340. 



