96 ON THE ANATOMY OF THE TOUCANS AND BARBETS. [Jan. 3, 



by a 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 pecuharly long 

 deltoid also occurs in the Passeres ; but its similar condition in the 

 Capitonidse has not, I think, before been observed. But, as showing 

 that the similarity in this respect of the Passeres to the Picidte and 

 their allies is not necessarily a mark of relationship, I may add that 

 in some other birds, as, e. g., Carpophaga, Ptilopus, and Gariama, 

 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 accessoria," 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 -, 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 Picidse, 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 com- 

 munication render the near relationship of the Picidse to the Capi- 

 tonidae even more certain than before. Nitzsch, from pterylographical 

 grounds, and Kessler '*, from osteological ones, long ago pointed out 

 this connection, which was afterwards remarkably confirmed by 

 Garrod's observations on their myology and visceral anatomy. 



The fact that there should be important cranial differences between 

 the two groups (and eveu amongst the members of one of these) only 

 shows that the cranial structure of a bird may be profoundly changed, 

 in accordance with its conditions of existence, whilst ia the rest of 

 its organs no change whatever is efifected ; and such a fact must of 

 itself tell heavily against the view that the structure of the skull in 

 birds is of itself alone a certain, or even sufficient, index to their sys- 

 tematic classification. 



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



* Tom. supra cit. p. 399. 



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



