COMMON PIGEON. 47 



toward its apex ; in the perfect condition of the parts the smaller inferiorly-placed 

 division of the muscle gave off two tendons 1 , one to the long and the other to the 

 short extensor plicae alaris anterioris ; the larger division passed over a smooth 

 facet on the humerus and over the coracoid head of the biceps to be inserted upon 

 the inwardly-looking surface of the great triangular tuberosity of the humerus. 

 Dorsally to the apex of the great pectoral we see a thin stratum of muscle in 

 relation internally with the crop and homologous with the deltoid of anthropotomy. 

 This muscle is divided into two strata by delamination. The superficial layer 

 consists of three parts, of which the first and most internally-placed joins the long 

 extensor of the anterior fold of the alar membrane ; the second and mesially-placed 

 joins the short extensor, whilst the third and dorsally-placed portion is inserted into 

 the outer aspect of the humerus from its middle down to a nodule at its lower 

 fourth marking the origin of the long radial extensor of the carpus. The deep 

 layer consists of one short muscle 2 innervated by the circumflex, arising from the 

 portions of the coracoid and scapula and of the ligaments in relation with the 

 shoulder-joint, and inserted into the upper surface of the humerus along a line 

 reaching from the apex of the triangular tuberosity receiving the tendon of the 

 great depressor humeri to the facet receiving the tendon of the great long levator. 

 Overlapped by this muscle, which acts as a levator humeri, and wedged between it 

 and the great pectoral depressor, is a second short levator humeri, innervated as is 

 the coracobrachialis, not as is the deltoid, arising from the coracoid and passing 

 down on the outer side of the tendon of the biceps to be inserted under the upper 

 portion of the tendon of the great pectoral. This muscle therefore should be con- 

 sidered to be a coracobrachialis. 



We have thus three muscles the 'pectoralis secundus,' or long levator; and 

 two shorter muscles, the former of which may be called ' deltoides externus,' and 

 the latter ' coracobrachialis brevis' entrusted with the work of raising the humerus, 

 but each with a distinct innervation. In some birds, e.g. Anser, the deltoides 

 externus passes into and takes an enlarged origin from the walls of \heforamen 

 triosseum^ and gains some mechanical advantage by availing itself of its pulley-like 

 outlet. 



In relation with the lower portion of the right coracoid may be seen two other 

 coracobrachiales (cut short in this preparation, but shown in situ at v and #, in 



1 The alar extensor muscles and many of the other muscles of the wing in Birds will be found 

 well figured and described in a monograph by Schoepss in Meckel's Archiv, 1829. Those of the 

 Pigeon are similarly figured and described by Macgillivray in his History of British Birds, i. pp. 34- 

 42, Plate iii, a work with which I was not acquainted when the first edition of this book was pub- 

 lished. Mr. Macgillivray remarks, p. 38, that the small muscular mass called by him retractor plicae, 

 and figured here, PI. ii. w', infra, had not been met with by him in any other birds except Pigeons. 



A doubling back of the tendon of the short alar extensor on to the nodule of origin of the long 

 radial extensor of the carpus has been shown by Professor Garrod to be characteristic of the true 

 Passeres. See P. Z. S. 1876, p. 509 ; Prof. Bell's translation of Miiller's Vocal Organs of the Pas- 

 seres, Appendix by Garrod, p. 64, Oxford, 1878. 



2 This muscle corresponds with No. 19, the Deltoides externus of Schoepss, as given in his 

 monograph on the Muscles of Flight in Birds in Meckel's Archiv for 1829, and is called 'levator 

 humeri ' by Tiedemann, and le petit releveur de 1'humerus ' by Vicq d'Azyr. It appears to have 

 been often confounded with the muscle next to be spoken of and lying close to it, which, though 

 similar in function and size, is differently innervated and quite separate from it. The latter muscle 

 is correctly described by Schoepss, I.e. p. 122, and named (No. 20) ' Deltoides inferior.' 



