CONNECTED WITH THE SHOULDER- JOINT. 121 



posterior and inner edge of the coracoid at about the middle of the 

 height of the bone, may be considered the homologue of the large 

 * coraco-brachialis superior' of gallinaceous birds 1 . A dense band 

 of ligamentous tissue (homologous probably with the praecoracoid 

 of the lizards) stretches in the coraco- clavicular membrane from 

 the sternal rostrum to the upper end of the clavicle ; and from it 

 a thin sheet of muscular fibres arises, which joins the tendon of 

 the pectoralis secundus in the pulley, as does also a slender slip of 

 muscle which passes from the mesoscapula. The main mass of the 

 pectoralis secundus is of a deeper colour, especially in young birds, 

 than these two latter muscles, which join its tendon ; and it is to 

 be remarked that the main mass, as well as the former of these 

 accessory slips, takes origin from the fibrous band in the coraco- 

 clavicular ligament. 



A ligament passes from the anterior external angle of the 

 coracoid at its sternal articulation (the 'epicoracoid' of Parker) to 

 be inserted on the sternum at a point about opposite the articula- 

 tion of the third sternal rib. It limits the fibres of the pectoralis 

 secundus mesially from those of the so-called ' subclavius ' (No. 

 xi. of Schoepss 2 ) externally, at the point where these latter pass 

 upwards and inwards to attach themselves to the base of the 

 coracoid. Inasmuch, then, as the two layers of the ' subclavius ' 

 of the bird are homologous serially with the two layers of the 

 intercostals, this ligament may be considered homologous with the 

 mesial attachment of the costo-coracoid membrane, which separates 

 the * subclavius ' of the mammal from the insertion of the internal 

 intercostals, the serial homologues of the deep layer of the sub- 

 clavius of the bird. 



Secondly, the nerve which supplies the pectoralis secundus of 

 the bird is obviously homologous with the nerve which supplies 

 the subclavius of the mammal, and not with the nerves which 

 supply the greater and lesser pectorals in that class. The nerve 

 to the bird's pectoralis secundus comes, in the Aecipiter nisus, 

 from the anterior factors and lower aspect of the brachial plexus ; 



1 The lower part of this latter muscle is aborted as far as its ordinary direction is 

 concerned, its upper part being represented by a very slender slip which arises from 

 the posterior aspect of the mesocoracoid region close to the glenoid, and, taking the 

 usual course of a coraco-brachialis, is inserted with the subscapularis. 



2 ' Beschreibung der Flugelmuskeln der Vogel,' von C. G. Schoepss, Meckel's 

 Archiv, 1829, p. 72. 



