114 ON THE HOMOLOGIES OF CERTAIN MUSCLES 



inner aspect of the coracoid and the inferior surface of the coraco- 

 clavicular membrane, from both of which structures it may receive 

 an accession of muscular fibres, it winds over a pulley formed for it 

 by the bone just mentioned, to be inserted between the insertion of 

 the great pectoral on the radial tuberosity of the humerus, internally, 

 and the tendon of the deltoid as it passes down to its attachment 

 on the outer aspect of the bone, externally. The tendon of the 

 levator humeri holding" thus an intermediate position between the 

 tendons of the deltoid and the great pectoral, may receive an 

 accession of muscular fibres from the mesoscapular portion of the 

 scapula ; or these fibres, which may have a separate nerve-supply, 

 may have also a separate insertion, from that of the levator, on the 

 humerus. But the pulley arrangement furnished by the coracoid 

 enables the levator in its simplest form to act as a powerful levator 

 of the humerus. 



The ' subclavius ' of anthropotomy arises from the cartilage of 

 the first rib, a region into the constitution or near neighbourhood 

 of which Mr. Parker has shown the epicoracoid to enter in several 

 mammals \ Under cover of a dense fascia (the ' costocoracoid mem- 

 brane,' which may be taken to represent in fibrous tissue 2 an aborted 

 large-celled cartilaginous band, which reached in the embryo from 

 the acromion to the presternum), the subclavius of man passes up 

 to be inserted into the costal surface of the outer half of the clavicle. 

 The relation held by this fascia to the muscle furnishes, as I shall here- 

 after strive to show, a most important means for differentiating the 

 pectoralis minor of the mammal from its subclavius. The variations 

 which the subclavius presents in anthropotomy cast light, as such 

 variations sometimes do, upon its homological representatives in the 

 lower animals. One of the most important of these variations is the 



1 See ' Shoulder-Girdle,' pi. 26, fig. 10, Mas decumanus ; fig. 5, Mus minutus; figs. 

 1 and 2, Mus musculus; fig. 5, Mus sylvaticus 



2 For the representation in fibrous tissue by adult structures of what was cartilage 

 in the embryo, see Parker, loc. cit. pp. 182, 184, 197, 198. For the existence of the 

 cartilaginous band, above mentioned, see Gegenbaur, ' Untersuchungen zur ver- 

 gleichenden Anatomie,' 1865, vol. ii. pp. 15-17, cited Parker, loc. cit. p. 223. 

 Prof. Pagenstecher, who however does not mention Prof. Gegenbaur's discovery, 

 speaks, in the description of the dissection of a drill, Mandrilla leucophaa ('Zool. 

 Gart.' April 1867, p. 128), of a very fine but strong elastic band, which ran along the 

 upper or anterior border of the pectoralis minor from the coracoid to the anterior end 

 of the second rib, as being the homologue probably of the coracoid of monotremes, 

 birds, and reptiles. 



