EEPORT ON THE SPHENISCID^. 73 



3. Ohliquus abdominis internus. 



Le 2Ktit oblique, Vicq d'Azyr, 1774, p. 490, No. 2. 



Der innere schrdge Bauchmunkel, Merrem. 



Der innere schrdge Bauchmuskel, Wiedemann, p. 80. 



V oblique interne, Cuvier, vol. i. p. 217. 



Der innere schrdge Bauchmuskel, Tiedemann, p. 296, No. 2. 



Muscle oblique interne de I' abdomen, Meckel, vol. vi. p. 19, No. 2. 



Obliquus internus abdominis, Owen, p. 30. 



Obliquus internus abdominis, Selenka, vol. vl. p. 103, No. 26. 



Le petit oblique de V abdomen, Gervais and Alix, p. 16. 



Attachments. — The internal oblique arises from tlie middle third of the external 

 border of the pelvic bone. The fibres pass obliquely forwards and downwards, and 

 are inserted into the lower two-thii"ds of the posterior border of the last vertebral 

 rib. 



Action. — This muscle co-oj)erates with the internal intercostal muscles in depressing 

 the ribs and diminishing the capacity of the abdominal and thoracic cavities. 



Relations.- — The muscle fills up the interval between the pelvic bone and the last rib. 

 Superficially it is concealed by the obliquus externus. Its deeper surface rests upon a 

 large air sac, which separates it from the subjacent transversalis abdominis. 



Nerve supply. — Branches from the last intercostal nerve. 



Variations.- — In Aptenodytes the origin of the muscle is limited to the anterior half of 

 the pubic bone, and its insertion extends to the last two vertebral ribs. In Pygosceles 

 the origin is confined to the ilium, and the muscle takes no attachment to the pubis. In 

 Eudyptes chrysolophus the muscle is inserted into the vertebral third of the last two ribs, 

 while in Spheniscus minor the internal oblique arises from the whole length of the pubic 

 bone, and not at all from the ilium. 



Remarks. — I have experienced considerable difficulty in deciding the synonymy of 

 this muscle. The description above given certainly corresponds more closely to that of 

 the quadratus lumborum {No. 9, p. 302) of Tiedemann, than to that of the obliquus 

 internus of that author. If, however, we assume that the internal oblique as above 

 described really corresponds to the quadratus lumborum of Tiedemann, we must conclude 

 that the obfiquus internus abdominis is absent in every species of Penguin. This con- 

 clusion, in view of the constant occurrence of the internal oblique in other birds, seems 

 so likely to be erroneous, that I prefer to believe that the obliquus internus of the 

 Penguin presents a somewhat unusual disposition rather than that it is entirely 

 wanting. 



(ZOOL. CHALL. EXP. — PART XVIII. — 1883.) S 10 



