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 ewtensor metacarpi radialis longior muscle. 
This is common to the Picide, 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 
Capitonide has not, I think, before been observed. But, as showing 
that the similarity in this respect of the Passeres to the Picidee 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 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 Picidz 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 Picide, Jndicator and other Pict 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 Picidee to the Capi- 
tonidze 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 even 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 in the rest of 
its organs no change whatever is effected ; 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. 
1 Zeitschr. f. ges. Naturwiss. 1862, xix. p. 400. 
2 Tom. supra cit. p. 399. 
3 Bull. Soc. Imp. Nat. Moscou, xvii. pp. 332-334, 340, 
