370 CLASS XVI. 



present an accumulation of the fleshy mass as close as possible to 

 the trunk, a disposition by which the muscles of the limbs have short 

 bellies with long tendons, which, especially in the legs, have a great 

 inclination to ossify. The great pectoral muscle is remarkably de- 

 veloped, surpassing in most birds all the other muscles collectively 

 in mass ; yet in the struthious birds it is small. This muscle draws 

 the humerus downwards, and thus is the principal moving power 

 in flying. The muscles that raise the arm-bone are less developed, 

 as the deltoid, which is usually described as represented by three 

 muscles, two of which however (m. deltoideus medius and inferior) 

 are regarded by RETZIUS as muscles of the scapula (musculus 

 supraspinatus and m. infraspinatus). The proper muse, deltoideus 

 arises from the ossiculum humero-scapulare and by a second head, 

 more downward and backward, from the anterior extremity of the 

 scapula; it is attached to the crest of the humerus 1 . Peculiar to 

 birds are the muscles with long tendons which stretch the dermal 

 fold, provided with elastic fibrous tissue, of the wings; for the 

 uppermost fold, between the upper-arm bone and the fore-arm, two 

 of these are seen; for the posterior fold, between the upper-arm 

 bone and the trunk, only one such tensor-muscle is present. The 

 abdominal muscles are thin and feeble; the rectus abdominis has no 

 transverse inscriptiones teydinece. Muscles corresponding to the 

 psoas and iliacus internus are usually not found in birds. The 

 muscles of the neck, in correspondence with its great mobility, are 

 strongly developed. The midriff is not indeed wanting in birds, 

 as was generally received formerly, but still differs greatly in them, 

 with the exception of Apteryx, from that in the mammal, being for 

 the most part aponeurotic and confined to the ventral surface of the 

 lungs 2 . 



1 On the horaology of the muscles of the anterior limbs in birds RETZIUS has pub- 

 lished some conclusions, in which amongst others he asserts that the so-named m. sub- 

 clavius does not correspond to the similarly named muscle of mammals, but ought 

 rather to be named costo-coracoideus or pectoralis minor. The muscle regarded as 

 pectorcdis minor is rather the homologue of the m. subclavius. See Forhandlingar vid 

 de STcandinaviske Naturforskarnes Mote i Stockholm, 184-2, pp. 659 664 (an extract in 

 MUELLER'S Archiv, 1844, s - T 5)- 



2 Compare on the muscles of birds, besides the general works of CUVIER, TIEDE- 

 MANN, MECKEL, &c., HEUSINGER in MECKEL'S Archiv f. d. Physiol. vn. s. 182 197, 

 Taf. 3 ; ScHOEPSS, Beschreibung der Flilgelmuskeln der Vogel in MECKEL'S Archiv f. 

 Anat. u. Physiol. 1829, ss. 72176; E. D' ALTON De Strigum musculis commentatio. 

 Halae, 1837, 4to. 



