30 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 70 



MUSCLES OF THE ABDOMEN 



The rectus ahdominis is a heavy muscle, but the origin is very 

 weak for its size, and is neither from the pelvic bone nor from a 

 definite aponeurosis descending cranio-ventrad, as is the case in 

 Kogia, and apparently Balaenoytera as well. Rather do the fibers 

 arise just craniad of the vulva from between the fasciculi of the 

 lateral abdominal muscles. Insertion is upon the caudal portion of 

 the sternum, and very likely from the costal cartilages adjoining. 

 The details of the origin of this muscle in Glohiocephala can not be 

 seen in the illustrations of this animal. 



The obliquus ahdominis extemus, with fibers running caudo-ven- 

 trad, has origin by bundles from a number of the more cranial ribs 

 about at the junction of the latter with their costal cartilages. The 

 caudal border of the muscle is on a line running from about the 

 twelfth thoracic vertebra to a point just craniad of the vulva, and 

 insertion is upon the sheath of the rectus abdominis. 



The ohliquus abdominis internus, with fibers running cranio-ven- 

 trad, arises from the deep dorsal fascia and several of the more 

 caudal ribs, including the sternal portions. Insertion is upon the 

 aponeurosis continuous with the rectus sheath. At its ventral termi- 

 nation it does not extend posterior to the vulva, and hence at this 

 point it is not located caudad of the external oblique. Its origin, 

 however, terminates about on a line dorsad to the anus. 



Both oblique muscles are apparently substantially similar' in the 

 other cetaceans considered. 



The transversus abdominis or transversalis, with fibers extending 

 caudo-ventrad, arises from the deep dorsal fascia investing the long 

 system of the back, and from the caudal border of the thorax along 

 the costal terminations. Insertion is upon the deep portion of the 

 rectus sheath and the tissue about the urino-genital orifices. This 

 muscle extends for some distance caudad of the abdominal obliques, 

 and to this extent differs from Kogia. 



Judging from the published descriptions it seems that the muscular 

 layers composing the abdominal walls of the Cetacea are somewhat 

 heavier than usual. 



VERTEBRAL MUSCULATURE 



Secondary hack muscles. — The trapezius group is lacking. The 

 latissimus dorsi is small and weak. Because of the condition of the 

 specimens the fibers of the original portion could not be followed 

 with satisfactory detail. It springs, however, by bundles from sev- 

 eral of the costae, and insertion is onto the medio-caudal part of the 

 humerus distad to its middle. This is essentially similar to the 

 condition in the other Cetacea discussed. 



