AVES. 



293 



weak, in consequence of the protection which the 

 extended sternum affords to the viscera of that 

 cavity. 



The External oblique (19) is chiefly remarka- 

 ble for the transverse arrangement of its fibres ; 

 these arise anteriorly by short fleshy digitations 

 from the inferior ribs, and by a large but very 

 thin tendon from the posterior ribs and the edge 

 of the ilium and pubis ; they are inserted by 

 aponeurosis into the anterior margin of the pubis, 

 and join the aponeurosis of the opposite 

 muscle in front of the thin and tendinous 

 rectus abdominis. This muscle, by drawing 

 downwards and backwards the posterior part 

 of the sternum and sternal ribs, opens the 

 angle between these and the vertebral ribs, 

 depresses, in consequence, the anterior part 

 of the sternum, and thus dilates the thorax, 

 and becomes a muscle of inspiration. 



The Internal oblique comes off fleshy from 

 the anterior moiety of the edge of the pubis, 

 arid tendinous from the posterior moiety of the 

 same bone ; it is much smaller than the pre- 

 ceding, and is directed forwards and inwards 

 to the last rib, which it draws backwards, and 

 thus assists the preceding in the compression 

 of the abdomen and abdominal air-cells, and 

 in the dilatation of the thorax. 



The Transversalis is a muscle of greater 

 extent ; it arises from the whole anterior margin 

 of the pubic bones by carneous fibres, and by 

 digitations from the three posterior ribs ; its 

 tendon unites with that of its fellow in the 

 mesial line, extends immediately over the pe- 

 ritoneum over the whole abdomen as far as 

 the posterior margin of the sternum to which 

 it is attached. 



The Rectus abdominis is not intersected by 

 tendinous digitations ; its origin is by a broad 

 thin tendon from the lower and posterior half 

 of the pubis ; at about the middle third 

 of the abdomen it becomes carneous, and 

 is inserted into the posterior margin of the 

 sternum. A mesial tendon or linea alba sepa- 

 rates the fleshy portions of the two muscles. 



The Diaphragm arises by fleshy digitations 

 from the sternal ribs; in the Ostrich these 

 digitations are five in number on either side : 

 the carneous fasciculi do not, however, extend 

 so far upon the central aponeurosis as even 

 to be united laterally to one another, and 

 consequently this muscle has frequently been 

 denied to birds. From the lungs being con- 

 fined to the back part of the thorax, the dia- 

 phragmatic aponeurosis attached to their inferior 

 surface is not extended as a transverse sep- 

 tum between the chest and abdomen, but allows 

 the heart to encroach upon the interspace of 

 the lobes of the liver, as in reptiles. The 

 contraction of the muscle tends directly to dilate 

 the lungs, but is less perfect as an inspiratory 

 action from the aponeurosis or central tendon 

 being perforated by large cribriform apertures 

 for the passage of the air into the abdominal 

 air-cells. 



The Wing-Muscles. The muscles of the 

 anterior extremity, especially those inserted into 

 the hum ems, are prodigiously developed, and 



form the most characteristic muscles of the 

 bird. The muscles of the shoulder, however, 

 are but small, and those of the distal segments 

 of the wing still more feeble. 



The Trapezius (20), the lower half of which 

 seems only to be present in birds, arises from 

 the spines of the lower cervical, and a varying 

 number of the contiguous dorsal vertebrae, and 

 is inserted into the dorsal margin of the sca- 

 pula and the corresponding extremity of the 

 clavicle ; the clavicular portion can commonly 

 be separated from the scapular. 



The Rhomboideus lies immediately beneath 

 the preceding, and is always single ; it passes 

 in a direction contrary to the trapezius from the 

 spines of the anterior dorsal vertebrae to the 

 dorsal edge of the scapula. 



The Levator scapula arises by digitations 

 from the transverse process of the last cervical 

 vertebra, and from the first two ribs ; it is inserted 

 into the posterior part of the dorsal edge of the 

 scapula, which it raises and pulls forwards. 



The Serratus magnus anticus (21) is most 

 developed in birds of prey ; it arises by large 

 digitations from three or four of the middle 

 ribs, and converges to be inserted into the ex- 

 tremity of the scapula. 



The Serratus parvus anticus or Pectoralis 

 minor, as it is termed in Man, arises by digita- 

 tions from the first and second ribs, and is in- 

 serted into the commencement of the inferior 

 margin of the scapula. This is the largest of 

 the muscles of the scapula in the Penguins. 



A muscle, which may be regarded either as 

 a portion of the Pectoralis minor or as the ana- 

 logue of the Subclavius muscle, arises from the 

 anterior angle of the sternum, and is inserted 

 into the external margin of the sternal extremity 

 of the coracoid bone. 



The Supra-spinatus (22) arises from the ante- 

 rior part of the outer surface of the scapula, and 

 is inserted behind the largely developed inter- 

 nal tuberosity of the humerus. 



The muscle which seems to represent both 

 the Inf'ra-spinatus and Teres major (23) has a 

 more extensive origin from the outer margin of 

 the scapula to its extremity, and is inserted 

 into the internal tuberosity of the humerus. 



The Subscapularis arises from the anterior 

 part of the inner surface of the scapula, and is 

 inserted into the humeral tuberosity. It is 

 divided into two portions by the Pectoralis 

 minor. 



The Latissimus dorsi (24, 24,) is but a feeble 

 muscle in this class, and is constantly divided 

 into two very distinct slips. The anterior por- 

 tion arises, more superficial than the trapezius, 

 from the spines of the four or five anterior 

 dorsal vertebrae, and is inserted near the tendon 

 of the deltoid into the outer side of the humerus. 

 The posterior slip comes from the spines of the 

 dorsal vertebrae above the origin of the glutaus 

 magnus, and sometimes from the anterior mar- 

 gin of the same muscle, and is inserted by a 

 broad and thin tendon immediately in front of 

 the preceding portion. 



The Deltoides (26) is comparatively a small 

 muscle ; it arises from the anterior part of the 



