MUSCULAR SYSTEM OF AVES. 91 



almost straight, parallel line, in their aponeurosis of insertion. 

 The fibres of this aponeurosis decussate those of the opposite side, 

 and adhere to the tendinous intersections of the rectus beneath. 

 The aponeurosis from the last rib passes to be inserted into a 

 strong ligament extending between the free extremities of the 

 pubic bones, leaving the abdomen, behind the last rib, defended 

 only by the internal oblique and transversalis. 



The ohliquus internus abdominis arises from the whole of the 

 anterior and outer surface of the pubis; aponeurotic from the 

 upper part, fleshy for half an inch from the lower or ventral 

 extremity : the carneous fibres run longitudinally, and cannot be 

 distinctly defined from the intercostales on their outer border, or 

 from the rectus abdominis on their inner or mesial border, which 

 forms the medium of the insertion of the internal oblique. 



The rectus abdominis is the medial continuation of the pre- 

 ceding muscle, which arises by a strong, flat, triangular tendon 

 from the lower or ventral extremity of the pubis and from the 

 inter-pubic ligament : it soon becomes fleshy ; the carneous por- 

 tion is interrupted by three broad, oblique, but distinct aponeu- 

 rotic intersections, and is finally inserted into the sternum. 



Transversalis abdominis. A layer of loose, dark-coloured cel- 

 lular tissue divides the internal oblique from the transverse abdo- 

 minal, except at its origin from the pubis, and for half an inch 

 anterior to that part. The transversalis then proceeds to derive 

 carneous fibres from the inner surface of the ribs near their lower 

 third; they pass obliquely upward and forward, and terminate 

 by a regular, slightly concave line midway between their origins 

 and the extremities of the ribs ; a strong aponeurosis passes thence 

 to the linea alba, but becomes thin at the pubic region, where a 

 mass of fat is interposed between it and the peritoneum. 



The diaphragm presents more of its mammalian character in 

 the Apteryx ' than in any other known bird. It is perforated by 

 vessels only, in consequence of the non-developement of the abdo- 

 minal air-cells. The origin corresponding to that of the lesser 

 muscle in Mammals is by two strong and distinct, short tendinous 

 pillars from the sides of the body of the last costal vertebra ; they 

 are united by a strong tendon or fascia, forming the anterior 

 boundary of the aortic passage. The tendinous pillars may be 

 traced forward for some way in the central aponeurosis, expanding 

 without crossing ; they are then lost in that aponeurosis, which is 

 perforated by the gastric arteries and veins, divides anteriorly to 



1 XI-. vol. ii. pi. 52 ; vol. iii. pi. 36, p. 287. 



